Pseudomonas tolaasii, causing brown blotch disease on cultivated mushrooms, and yielding a white line precipitate towards P. "reactans", has been shown to induce lysis of erythrocytes. Some Finnish strains isolated from diseased mushroom fruit bodies, although harboring the typical features of P. tolaasii, proved to be distinct, and have been allocated to a nov. sp. P. costantinii. We examined in these study whether all brown blotch causing agents were hemolytic. The induction of erythrocytes lysis seemed to be a rather common feature of mushroom associated-pseudomonads, especially for strains involved in the production of a white-line-in agar.