In this study the clinical significance of serum ferritin (SF) determinations was evaluated in patients with disseminated non-seminomatous germ cell tumors (NSGCT). The SF levels during the presence of active tumor but before institution of combination chemotherapy (cis-platinum, vinblastine and bleomycin, PVB) were within the normal limits in 38/47 NSGCT patients. During PVB treatment peaking SF levels were observed in relationship to the drug administration, whereas alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) serum levels decreased continuously. Other drugs also caused temporary increases in SF levels. Tumor recurrence was not recognized by SF increases in all eight patients tested. Based on the results we conclude that serial SF determinations are of no value in monitoring patients with NSGCT.