The lipases produced by Pseudomonas have a wide range of potential biotechnological applications. Pseudomonas aeruginosa IGB83 was isolated as a highly lipolytic strain which produced a thermotolerant and alkaline lipase. In the present work, we have characterized the P. aeruginosa IGB83 gene (lipA) encoding this enzyme. We describe the construction of a lipA mutant and report on the effect of two carbon sources on lipase expression.