The antimicrobial efficacy, general and local tolerance of a new intramuscular application form of trimethoprim/sulfamethoxazole was evaluated in a French-German clinical study. Fifty-five urological patients with urinary tract infections were treated with two i. m. injections (3 ml) daily over three to five days followed by oral medication. The study revealed excellent antimicrobial efficacy of the drug. In general TMP/SMZ was tolerated well after i. m. administration. Elevation of creatinine phosphokinase was observed in only three patients treated i. m. for five days. The high viscosity of the solution renders i. m. injection technically difficult, leading to a high proportion of local complications. The indications for use of i. m. administered TMP/SMZ in the hospital are limited, however it should be suitable for private practitioners in that an effective antimicrobial treatment can be started which can be continued by oral or intravenous medication.