Production of protein A by 100 various animal strains and 106 human strains of Staphylococcus aureus has been detected by conditioned haemagglutination after growth on seven different culture media: agar medium at n degrees 2 and Columbia agar with and without nalidixic acid (10.8 micrograms/ml), Baird-Parker, Chapman and tellurite-glycine-agar media. Rate of protein A-producing strains is as high on nalidixic acid media as on the same media without antibiotic. Baird-Parker, Chapman and tellurite-glycine-agar media are not convenient for protein A detection.