Kumiai Chemical Industry Co., Ltd v Kenso Corporation (M) Sdn Bhd [2026] FCA 1219 (Rofe J, 26 August 2026)
Australia’s best method requirement continues to punch above its weight as a ground of invalidity. Two decisions this year illustrate the point. In April, the Full Court in The NOCO Company v Brown and Watson International Pty Ltd [2026] FCAFC 44 confirmed that, for a divisional application, the patentee’s knowledge is assessed at the filing date of that divisional, not the parent. We previously discussed the consequences of that decision, and the difficulty of curing a best method defect after grant in our earlier article Can NOCO restart a best method NO GO in Australia?
The recent interlocutory decision by a single judge of the Federal Court in Kumiai v Kenso illustrates a related risk. It is not about divisionals. It is about what happens when a specification sells the invention as industrially advantageous but only exemplifies it at laboratory scale.
What the Court decided
Kumiai asserted an innovation patent directed to a process for producing the herbicide pyroxasulfone. Kenso sought leave to amend its cross-claim to allege that the patent failed to disclose the best method known to the patentee.
The proposed case was relatively straightforward. The specification repeatedly described the invention as being “industrially advantageous”, “advantageous for production on an industrial scale” and “suitable for industrial manufacture”. However, the examples disclosed only laboratory-scale experiments. Kenso contended that Kumiai, as the commercial manufacturer of the Sakura® pyroxasulfone product range, must have known an industrial-scale process that had not been disclosed in the specification.
Why the decision matters
Perhaps the most significant aspect of the decision is that the Court accepted that a challenger need not identify the undisclosed best method with precision before advancing the allegation of lack of best method. Consistent with the Full Court’s reasoning in Zoetis v Boehringer Ingelheim, it was sufficient at this stage to allege that the patentee knew of a better method which had not been disclosed.
The decision also highlights the importance of how the invention is characterised. Kumiai argued that the invention was directed to solvent selection. Kenso argued that it was an industrially advantageous manufacturing process. Justice Rofe declined to resolve that dispute at the interlocutory stage, but noted that the repeated references to industrial-scale production in the specification could form part of the invention as described.
A further noteworthy aspect is the Court’s willingness to infer the existence of undisclosed industrial know-how from surrounding circumstances. Evidence that Kumiai was manufacturing commercial pyroxasulfone products at or around the filing date, coupled with statements in the specification regarding industrial-scale production, was sufficient to make the allegation arguable.
Why best method remains a powerful ground of attack
Best method occupies a unique place in Australian patent law. However, the drafting and disclosure issues that underpin best method disputes are equally relevant to global patent portfolios.
Unlike novelty or inventive step, the inquiry focuses on what the applicant actually knew at the filing date. The most relevant evidence often lies within the patentee’s own organisation rather than in the prior art.
It is also a defect that can be difficult to detect during examination and opposition proceedings, yet potentially fatal once established in litigation. As we noted in our earlier NOCO article, best method is ultimately concerned with the patent bargain. Where an applicant seeks a monopoly for an invention, Australian law requires disclosure of the best way known to perform it.
The decision further illustrates the procedural leverage a best method allegation can provide. Justice Rofe accepted that discovery concerning the patentee’s manufacturing processes may be relevant to both infringement and best method, potentially giving challengers access to information that would not otherwise be in issue.
Practical lessons
The decision reinforces several practical drafting points.
First, caution should be exercised when making broad statements that an invention is commercially suitable, industrially advantageous or capable of industrial-scale manufacture. If those advantages are emphasised, consideration should be given to whether the specification adequately discloses how those outcomes are achieved.
Secondly, best method should not be viewed as a one-off enquiry undertaken at the provisional filing stage. The question should be revisited whenever a complete, PCT or divisional application is filed. Following NOCO, knowledge acquired between filings may become highly relevant.
Finally, where a client has developed commercially valuable manufacturing know-how that it may prefer not to disclose, careful consideration should be given to whether patent protection remains the preferred strategy, or whether aspects of the process are better maintained as trade secrets.
Looking ahead
Kumiai v Kenso is not a final determination on validity. However, it is a timely reminder that the best method requirement remains a potent ground of attack in Australia.
For patentees, the message is clear: if a specification promotes an invention as being suitable for industrial-scale manufacture, the disclosure should support that promise. Laboratory-scale examples coupled with broad statements of commercial or industrial applicability may invite scrutiny as to whether the best method known to the applicant has truly been disclosed.
For challengers, the decision demonstrates that a best method case may be available even where the alleged undisclosed method cannot yet be identified with precision. Where there is evidence of commercial manufacture at or around the filing date, courts may be prepared to permit the allegation to proceed and allow the underlying facts to be explored through discovery.
