A cell-free crude extract containing the white line inducing principle (WLIP), a lipodepsipeptide produced by Pseudomonas 'reactans', could inhibit browning of mushrooms caused by Pseudomonas tolaasii. Mushrooms inoculated with Ps. tolaasii at concentrations of 2.7 x 106 cfu ml-1 or higher showed the symptoms of the disease after 2 d of incubation. Mushroom caps treated with various concentrations of a crude WLIP preparation, and later inoculated with bacterial concentrations higher than the threshold value, did not develop the symptoms of the disease. One milligram of a crude WLIP preparation could block 50% of the symptoms caused by 1.2 x 107 cfu. The inhibition of browning was effective when incubating at low temperatures for 4 d. A suspension containing 1.6 mg ml-1 of pure WLIP was also able to inhibit the symptoms of brown blotch disease induced by 7.6 x 106 cfu ml- 1 of Ps. tolaasii.