The respondent was the patentee of South African Patent 92/4018, entitled ‘Process and Compositions for the Disinfection of Waters’, relating to a process for killing microorganisms and controlling biofouling in high chlorine demand circulating waters by mixing a chlorine precursor with an ammonium salt to form a chloramine biocide and adding it to the water system. The respondent sued the appellant for patent infringement in the Court of the Commissioner of Patents. The appellant counterclaimed for revocation of the patent on the grounds of lack of novelty and lack of inventive step under the Patents Act 57 of 1978. The court a quo dismissed the counterclaim and granted an interdict against infringement. On appeal to the Supreme Court of Appeal, it was common cause that the appellant infringed the patent if it was valid, and the appeal focused on whether claims 1 and 14 involved an inventive step.