Our study describes the production, purification and properties of an enzyme from Pseudomonas aeruginosa displaying the properties of phospholipase A. Maximal amounts of enzyme could be detected in the culture supernatant when the bacterium was grown for 3 to 5 days at 37 degrees C in stirred flask cultures containing brain heart infusion. The enzyme was purified by polyethylenimine precipitation and ammonium sulfate precipitation followed by gel filtration. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the enzyme preparation exhibited two bands with molecular weights of 13.5 and 60 kD, respectively. Correspondingly, two peaks of the same molecular weight could be demonstrated by high performance size exclusion chromatography. The activity toward the sn-2 ester binding of phospholipids was characterized and found to be highest towards phosphatidylcholine. Enzymatic activity was not influenced by the addition of calcium or EDTA while magnesium and strontium caused a decrease of activity. The lyophilized enzyme was found to be stable when stored at -70 degrees C and most active at pH 8.0.