Minimal inhibitory (MIC) and minimal lethal concentrations (MLC) of ampicillin, mezlocillin, piperacillin, cephalothin, cefamandole cefoxitin, cefuroxime, cefotaxime, gentamicin, and doxycycline against 44 strain of Listeria monocytogenes from clinical specimens were determined by broth dilution tests. With regard to the MIC90 and MLC90 values (concentrations which inhibited or killed 90 percent of the strains) ampicillin showed the greatest anti-listeric activity with 0,48 and 20,8 microgram/ml. The corresponding results for mezlocillin were 8,0 and 54,4 microgram/ml, for piperacillin 5,2 and 128 microgram/ml, resp. Among the cephalosporins, cephalothin showed the best activity (MIC90, 5,8 microgram/ml, MLC90, 76,8 microgram/ml). The MIC90 values of cefamandole and cefoxitin were 7,8 and 89,6 microgram/ml, resp. and the MLC90 was more than 128 microgram/ml while there was no clinically relevant activity of cefuroxime and cefotaxime (MIC90 more than 128 microgram/ml). The MIC90 and MLC90 results of gentamicin were 12 and 15,2 microgram/ml, resp, and those of doxycycline 8 and 25,6 microgram/ml, resp. There were only slight differences between gentamicin MIC and MLC values. Henceforward the drug of choice for the treatment of generalized listeric infections should be ampicillin eventually in combination with gentamicin.