The in vitro activities of imipenem (formerly imipemide, N-formimidoyl thienamycin, or MK0787) and amikacin in combination with cefotaxime, trimethoprim-sulfamethoxazole, and each other were tested against 26 Nocardia asteroides strains. The agar dilution method was used for all tests. Synergy was present in 80% of tests with imipenem-trimethoprim-sulfamethoxazole, in 92% of tests with imipenem-cefotaxime, and in 83% of tests with amikacin-trimethoprim-sulfamethoxazole. Indifference was found on rare occasions, and no antagonism was seen.