The paper reports a study of the activity of cefotaxime and its metabolite, desacetylcefotaxime, and the association of the two compounds, against 699 strains of enterobacteria, staphylococci and Bacteroides fragilis of hospital origin. The results of the study confirm the good activity of the drug and the less satisfactory activity of its metabolite, which is nevertheless comparable to second generation cephalosporins. The 1:1 association of the two compounds showed synergism in percentages ranging from 3.7% to 15% of strains, and partial synergies of indifference to the remaining strains. Antagonisms were only observed against some M. morgani and H. alvei strains.