Treatment of in vitro cultured Ehrlich ascites carcinoma cells with cisplatin, daunomycin, doxorubicin, cytosine arabinoside, 3'-fluorodeoxythymidine, colchicine and vincristine in cytostatically effective concentrations results in significantly increased levels of the small stress protein, hsp25, as analyzed by immunoblotting. However, no induction of hsp25 could be detected after treatment of the tumour cells with 5-fluorouracil, aminopterin, amethopterin, mithramycin and cyclophosphamide. None of these cytostatic drugs induces hsp70.