The effects of yemenimycin on the growth and contents of DNA, RNA and proteins of Candida albicans were appraised. Glycolysis and aerobic respiration were less sensetive to the antibiotic than the syntheses of nucleic acids and proteins. Incorporation of P-32 in DNA and RNA was markedly arrested by yemenimycin whereas the contents of the labeled supplement in TCA soluble fraction and phospholipids were appreciably augmented. Yemenimycin restricted the incorporation of C14-thymidine and to a lesser extent of C14-uridine in Bacillus subtilis cells while the incorporation of H3-lysine in cellular protein was relatively the most resistant. Synthesis of aminoacyltRNA and the binding of C14-phenylalanyl-tRNA to ribosomes in response to poly U were found to be rather insensitive to the drug. Finally the effect of yemenimycin on the protein synthesis of intact rabbit reticulocytes and their cell-free system was assessed. The antibiotic could influence unfavorably the synthesis of protein.