Peritoneal hyperthermia may have a role in limiting serosal metastatic disease. When applied to the peritoneal cavity immediately after surgery, it is important to know the optimum temperature, and to investigate the subsequent healing of intestinal anastomoses. To study the first problem, local hyperthermia was applied to the intestinal loop of rats for 30 min. Treatment at 46.0 degrees C or 45.0 degrees C resulted in 100 per cent and 90 per cent mortality respectively, but 100 per cent survival was obtained at 44.0 degrees C. To study the second problem rats with intestinal anastomoses were studied in three groups: group A, local hyperthermia (44.0 degrees C x 30 min) applied to the intestinal loop containing the anastomosis; group B, local hyperthermia (44.0 degrees C x 30 min) applied using saline supplemented with mytomycin C (10 mg/l); group C (controls) no thermal treatment was applied. Anastomotic healing was assessed by breaking strength and histological examination. On the third day after operation, the breaking strength of anastomoses decreased to the lowest values in each group, but no statistically significant differences were noted. On the seventh and 14th day, increased resistance to breaking developed in all three groups and was greatest in the thermally treated groups. Histological findings supported these results. Local hyperthermia up to 44.0 degrees C x 30 min had no adverse effects on the healing of intestinal anastomoses.