Important Update on Australia's Flip-Flopping "Best Method" Requirement for Divisional Patent Applications

Key Takeaways

• Full Court rules best‑method date is divisional filing date.
• Decision overturns earlier view that parent filing date applies.
• Creates higher invalidation risk for Australian divisional patents.
• Aligns Australia with other jurisdictions lacking best‑method requirement.

Pulse Analysis

Australia remains one of the few jurisdictions that still enforces a “best method” disclosure under s 40(2)(aa) of the Patents Act 1990. While most major patent systems have abandoned the requirement, Australian law obliges applicants to disclose the optimal way of performing the invention in the complete specification. Historically, courts debated whether the relevant date for this disclosure was the parent’s filing date or the divisional’s own filing date, leading to inconsistent rulings that confused practitioners worldwide.

The Full Court’s recent decision in The NOCO Company v Brown and Watson International (2026) settles the debate by anchoring the best‑method assessment to the divisional filing date. By interpreting the statutory language to refer to the applicant of the divisional, the bench rejected earlier Federal Court reasoning that linked the requirement to the parent application. This creates a stricter evidentiary standard: any improvement discovered after the parent filing must be incorporated in the divisional or risk rendering the patent vulnerable to revocation. Compared with the United States, Europe, and Japan—where the best‑method clause has been repealed—the Australian approach now imposes a unique compliance hurdle for domestic and foreign filers.

Practitioners must adapt quickly. Drafting strategies should include proactive monitoring of technical developments up to the divisional filing moment, and, where feasible, filing continuations that capture the latest know‑how. Companies may also consider consolidating inventions into a single application to avoid the divisional trap, or lobbying for legislative change to harmonise Australia’s patent framework with international norms. The decision is likely to spur renewed debate in the IP community about the practicality of the best‑method requirement and could prompt future reforms aimed at reducing uncertainty and aligning Australia with global best practices.