The effectiveness of sulfamethoxazole (SMZ; 13 patients), trimethoprim (TMP; 23 patients), and the combination of both (39 patients) in therapy for acute urinary tract infections after major gynecological operations has been studied. Plasma concentrations of TMP and SMZ were measured on the 1st and 5th days of treatment before as well as 4, 7 and 12 h after administering the drugs. No difference was found between TMP and TMP/SMZ, although there are minor differences in the antibacterial spectrum. Treatment with TMP alone is superior to the combined regimen due to a smaller incidence of side effects; thus, in addition to the combination with SMZ, introduction of TMP alone on the market is recommended.