The in vitro activity of cefotaxime (HR 756) was tested in comparison with cefuroxime, cefamandole, cefoxitin, cefazolin, ampicillin, mezlocillin, gentamicin and amicacin. MIC values were investigated on 168 freshly isolated gram-positive and gram-negative bacteria from clinical sources. Enterococci and Pseudomonas aeruginosa behaved cefotaxime-resistant. All the other species examined showed a very good sensitivity range against cefotaxime. Cefotaxime was the most active antibiotic of our study.