Two hundred and forty-four clinical and environmental strains of nine species of halophilic vibrios isolated in Hong Kong were tested for their susceptibilities to 23 antimicrobial agents by an agar dilution method using unsupplemented Mueller-Hinton agar, an inoculum size of 10(5) cfu per spot and incubation for 18 h at 30 degrees C. Most strains were resistant to sulphamethoxazole, trimethoprim, penicillins and older cephalosporins, and most were susceptible to chloramphenicol, tetracycline, cotrimoxazole, the aminoglycosides, the newer cephalosporins, aztreonam, imipenem and the quinolones. However, there were significant differences between species, especially in their patterns of beta-lactam susceptibility.