In order to elucidate the mechanism of elevation of α-fetoprotein (AFP) which we often observed during VAB-6 chemotherapy, we analyzed sequential changes of AFP, liver enzymes and bilirubin in 10 patients with evaluable disseminated testicular cancer who were treated with VAB-6 chemotherapy. None of the patients had previous liver disease or hepatic involvement. During the early phase of each course of chemotherapy, AFP showed a temporary elevation associated with reversible increase in liver enzymes and bilirubin. These changes returned to normal before the next course of chemotherapy. In each patient, marked tumor regression occurred as a result of VAB-6 chemotherapy. Nine of the 10 patients remain free of disease after treatment. We conclude that during VAB-6 chemotherapy, a temporary elevation of AFP is common, associated with reversible liver dysfunctions, and that this spurious elevation of the tumor marker, most likely caused by a heavy dose of cisplatin, should not be interpreted as related treatment failure