The production of lipase and protease from psychrotrophic strains of Pseudomonas fluorescens may result in spoilage of dairy products. The lipase (lipA) and alkaline metalloprotease (aprX) genes of P. fluorescens B52 are regulated by temperature and are located at opposite ends of an operon which contains eight genes and spans 14 kb. In this report, we show that lipase activity in the supernatant of cultures of P. fluorescens strain B52 is also regulated by the homologue of the Escherichia coli EnvZ-OmpR two-component regulatory system. Differences in the regulation of lipase and protease may be related to the proximal and distal locations of aprX and lipA within the operon.