The effect of bleomycin (BLM) on a murine fibrosarcoma, FSa-II, was investigated at elevated temperatures. Animals were C3Hf/Sed mice derived from our defined flora mouse colony. Single-cell suspensions of the tumour were transplanted into the murine foot. Tumours with an average diameter of 4 mm were treated in a water bath where a desired temperature was maintained. Some animal groups received an intraperitoneal injection of glucose 60 min before hyperthermia to reduce tumour tissue pH. Hyperthermia was given for 60 min at 41.5 degrees C, 30 min at 43.5 degrees C, or 60 min at 43.5 degrees C, and tumour growth (TG) time to reach 1000 mm3 was studied. BLM treatment at 41.5 degrees C for 60 min prolonged the TG time compared to BLM treatment at a room temperature. The identical prolongation was observed following BLM treatment given at 43.5 degrees C for 30 min, although the growth prolongation was greater following BLM treatment given at 43.5 degrees C for 60 min than the other two treatments. This greater prolongation is probably attributable to an additive effect; namely hyperthermia of 43.5 degrees C for 60 min induces substantial lethal damage by itself while the other two heat treatments do not induce significant damage. It is interesting to note that this kind of enhancement was observed at a low temperature of 41.5 degrees C. A glucose injection before BLM and hyperthermia treatments further enhanced tumour response. These observations agree with our previous observations following in vitro treatments of the same tumour cells, and indicate that BLM is a good drug to be combined with hyperthermia.