Systemic exposure to melphalan is minimized during isolated limb perfusion (ILP) by isolating a limb from the rest of the body. Consequently, there should be no toxicity to vital organs. At present systemic toxicity after ILP has not been studied in detail. Therefore, the incidence, nature and risk factors of systemic toxicity was retrospectively studied in 368 patients who underwent a single ILP with melphalan between 1978-1990. Some form of systemic toxicity occurred in 98 patients (27%). Nausea and vomiting after the 1st post-ILP day was seen in 73 patients (20%), and in seven (2%) treatment was required. Bone marrow depression was encountered in seven patients (2%): WHO grade II in five, and grade III in two. Miscellaneous systemic side-effects, including fever and minimal scalp hair loss, occurred in 19 patients (5%). Leakage from the isolated circuit to the systemic circulation was measured with radioactive tracers. Mean cumulative leakage during ILP was 0.9%. Systemic toxicity was not increased in patients with leakage greater than 1% or 5%. Female sex was associated with an increased incidence of systemic toxicity (P<0.05). Age over 60 years (P<0.05) and more severe acute regional toxicity (P<0.05) were correlated with nausea and vomiting. The miscellaneous systemic side-effects were more frequently encountered in women than in men (P<0.05). In conclusion, systemic toxicity was rarely severe, with nausea and vomiting being the most frequently encountered side-effects. Age over 60 years, female sex and more severe acute regional toxic reactions were correlated with an increased incidence of systemic side-effects. Systemic leakage during ILP was not associated with toxicity, probably due to the low incidence of significant leakage.