This phase I/II study evaluated the feasibility, toxicity and response rates of von Ardenne's systemic cancer multistep therapy (sCMT) when applied as an adjunct to cytostatic therapy in patients with metastatic colorectal cancer. sCMT consists of whole-body hyperthermia (WBH) at 41.8-42.1°C, hyperglycaemia and hyperoxaemia. All patients who entered the trial first received three monthly courses of chemotherapy (folinic acid, 50 mg, days 1-5; 5-fluorouracil, 425 mg/m2, days 1-5; mitomycin 8 mg/m2, day 1), followed by response evaluation according World Health Organization (WHO) criteria. Responders (partial/complete remission) were assigned to three further courses of chemotherapy, whereas non-responders (stable/progressive disease) were allocated to additional sCMT on day 1 of every subsequent chemotherapy course. The WBH procedure was administered under general anaesthesia employing the Iratherm-2000 radiant heat device. Of 28 patients enrolled, 19 received more than three treatment courses. Eight of these 19 patients had responded to chemotherapy (PR) and thus obtained three further courses of chemotherapy alone. In 10 of 19 patients who had not responded (SD, PD), three additional courses of chemotherapy were combined with sCMT (with 25 sCMT applications). One patient who did not respond to initial treatment declined sCMT and was continued with chemotherapy alone. It was found that sCMT was feasible, but associated with a specific spectrum of grade III/IV toxicity (skin 20%, pain 16%, peripheral nerves 8% of treatment courses). The fact that three patients who did not respond to initial chemotherapy achieved a PR after additional sCMT suggests that sCMT may enhance the effect of chemotherapy in patients with colorectal cancer.