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 × 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 × 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 × 106 cfu ml−1 of Ps. tolaasii.