The in vitro antimicrobial activity of streptomycin, rifampicin, tetracycline, seven nonsteroidal anti-inflammatory agents (acetyl-salicylic acid, piroxicam, indomethacin, ibuprofen, ketoprofen, sulindac, and diclofenac), and eight phenotiazine derivatives and antidepressant agents (clorpromazine, fluphenazine, amitryptiline, clomipramine, imipramine, maprotiline, sertraline, and diazepam) against 62 strains of Brucella spp. was tested. Diclofenac was the most active of the anti-inflammatory agents (MIC90 = 16 micrograms/ml). The activity of the phenotiazines and antidepressants was heterogeneous, with MIC90s ranging from 16 micrograms/ml for sertraline and 32 micrograms/ml for fluphenazine and clomipramine to > 512 micrograms/ml for diazepam. When the six most active anti-inflammatory agents and the six most active psychiatric drugs were tested at pH 5 and pH 4, the MICs remained unchanged except for those of fluphenazine; the MIC50 and MIC90 of this agent increased by one dilution.