Propionibacterium acnes was grown in continuous culture in the presence of propylene phenoxetol. At sub-lethal concentrations of this antimicrobial agent (0.025-0.1% w/v) steady-state growth conditions were achieved. In comparison with the control, cell biomass, maximum specific growth rates and levels of the extracellular lipase and hyaluronate-lyase, decreased with increasing concentrations of propylene phenoxetol. Levels of protease activity remained approximately constant whilst production of acid phosphatase was significantly increased with increasing propylene phenoxetol concentrations. At the highest concentration of the antimicrobial agent (0.2% w/v) growth was completely inhibited.