Interactions of hyperthermia with carboplatin, cisplatin and etoposide were investigated in vitro in JM, a human, T cell, lymphoblastic cell line. Thermal enhancement ratios (TER) for carboplatin killing increased with temperature (2.3 at 40.5 degrees C, 3.2 at 41.8 degrees C) and were similar to those for cisplatin killing (2.6 at 40.5 degrees C, 3.6 at 41.8 degrees C). In a separate experiment, cytotoxicity was additive when carboplatin and cisplatin were given simultaneously at 37 degrees C and at 41.8 degrees C. Etoposide, which synergizes with platinum agents, did not have supra-additive cytotoxic interactions with hyperthermia. The data presented are relevant to the conduct of clinical hyperthermia trials.