Ten Chinese patients were reviewed, all with mediastinal germ cell tumours and treated in our centre during the past 8 years. Three patients with pure seminomas were given chemotherapy with or without radiotherapy. AB achieved complete remission with no relapse. Seven patients with non-seminomatous germ cell tumours (NSGCT) were given chemotherapy, with or without surgery. Two patients with rapid decay of alpha-fetoprotein (AFP) levels (half-life less than or equal to 7.2 days) during chemotherapy achieved complete remission with no relapse. Five patients with prolonged decay of AFP levels (half-life > 7.2 days) failed to achieve complete remission with initial chemotherapy and all but one patient died between 5 and 9 months later. One patient developed acute megakaryocytic leukaemia. Using isoelectric focusing, AFP bands specific to NSGCT were quantified, and comparison was made with the total AFP in five cases. In each case the change in NSGCT-specific AFP concentration in response to therapy closely paralleled that of total AFP. Estimation of NSGCT-specific AFP offers no apparent advantage in monitoring disease response or progression.