The effect of cibacron blue 3G-A (CB) on bacteriolysis induced by penicillin G was investigated using Staphylococcus aureus FDA 209P. Penicillin-induced lysis was completely inhibited by 30 microM CB. However, the bactericidal effect of penicillin G was not influenced by CB. These results indicate that a bacteriolytic process is not essential for penicillin to kill S. aureus.