Physiological regulation of the extracellular lipolytic activity of the Pseudomonas aeruginosa isolate IGB 83 was investigated by growing the bacteria with different carbon sources. Glycerol and triacylglycerols induce lipolytic activity, while glucose or acetate do not. The optimum temperature for the extracellular lipolytic activity was found to be 55-degrees-C while maximal activity was found at pH 10. The activity half-life at pH 8.5 and 55-degrees-C was 13 min. The lipase was purified from the culture supernatant and had an apparent molecular weight of 58 kD and an isoelectric point of 8. The biochemical characterization of the alkaline and thermoresistant lipolytic activity and a comparison with the reported characteristics of other enzymes clearly shows that this enzyme constitutes a novel lipase.