Scanning electron microscopy of changes in bacteria induced by antimicrobial agents which interfere with cell wall synthesis revealed morphological alterations which correlated well with their mechanism of action. The present studies were undertaken to investigate the presence and characteristics of alterations in surface morphology resulting from the action of antibiotics known to interfere with intracellular protein synthesis. Strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were exposed to kanamycin, chloramphenicol, and tobramycin during various phases of bacterial growth. A spectrum of morphological changes related to concentration of drug and duration of exposure was observed which was similar to those induced by penicillin or cephalothin. Cells were also exposed to sulfamethoxazole with similar results. The morphological abnormalities observed may be surface reflections of specific abnormalities of intracellular protein synthesis or may represent a final common pathway of druAg-induced injury at many sites within or on bacterial cells.