A hyper-thermostable, alkaline lipase from a newly-isolated, mesophilic Pseudomonas sp. was optimal at pH 11 and at 90 degrees C. It had a half-life of more than 13 h at 90 degrees C. It was activated by 30% when heated at 90 degrees C for 2 h. The enzyme had a greater affinity for mustard oil (K-m = 40 mg ml(-1)) than for olive oil (K-m = 140 mg ml(-1)).