The normal human epidermal keratinocyte (NHEK) was used to evaluate the cytotoxicity of recombinant lysostaphin. As determined with the Neutral Red (NR) cytotoxicity assay, the midpoint toxicity value (NR50) after 48 h exposure was 16 +/-0.4 g lysostaphin/l. Lysostaphin cytotoxicity effect is much less than the surface active agent, sodium laurate. However, the NR,, value after 48-h exposure was 1.9 +/- 0.02 g/l for S. aureus lysate derived from the bacterial lytic action of lysostaphin. A linear increase in interleukin-8 (IL-8) level in NHEK cells from resting levels of 65 +/- 3 pg/ml to peak of 760 +/- 15 pg/ml during the first 9 hours was noted for the cells treated with 800 mg lysostaphin/l. S. aureus lysate has the same effect on the induction of IL-8 levels. The induced rises in IL-8 were lysostaphin and S. aureus lysate concentration dependence.