The stability of mRNA for the 8-lysin of Staphylococcus aureus was determined by measuring the residual lysin synthesis after inhibition of DNA-dependent RNA polymerase activity with rifampin. At the late logarithmic-early stationary phase of growth the 5-lysin mRNA was very stable, with a half-life of ca. 20 min. Total cellular RNA was extracted from S. aureus and translated with a modified Escherichia coli S-30 system; 8-lysin was identified amongst the translation products by immunoprecipitation and immunoabsorption. The 8-lysin synthesized in vitro was of a size similar to mature 5-lysin and did not require a signal sequence for secretion from the cell.