Physiological effects of NaCl concentration (equivalent water activities, a(w), 1 to 0.87) were investigated with the moderately halophilic and piezotolerant bacterium, Kocuria rosea (formerly Micrococcus roseus), grown in bacteriological peptone/yeast extract broth. This bacterium, which was isolated from open shallow seawater, can grow in 150 g NaCl l(-1) (optimum NaCl concentration: 30 g l(-1), a(w)=0.984) and under 207 MPa of hydrostatic pressure. The effects of water activity on mu(m) can be quantitatively predicted, to a high level of accuracy by application of the Aiba/Edwards, and the Levenspiel-type unstructured inhibition-type kinetic models.