This study investigated the use of late dose intensification therapy (LDIT) with cyclophosphamide (180 mg/kg) and VP 16 (1 g/m2) plus autologous bone marrow rescue in 22 patients with small cell lung cancer (SCLC). These patients were selected from a group of 95 patients who received three courses of a five-drug induction regimen comprising cyclophosphamide (750-1000 mg/m2), adriamycin (40 mg/m2), VP 16 (100 mg/m2) for 3 days, methotrexate (50 mg/m2) and vincristine (2 mg) (CAVMO). There were 16 patients with limited disease, 8 of whom were in complete remission (CR) and 8 in partial remission (PR) after the induction therapy. The other 6 patients had extensive disease; 3 of these achieved CR and 3 PR after induction therapy. Of the 11 patients in PR, 5 responded to LDIT; 3 had a further PR, and 2 CR. Subsequent to LDIT radiotherapy 4000 cGy was given to the primary site in 10 of the 22 patients. Since the start of the study, 19 of the 22 patients have relapsed and died (median survival 11 months), while 3 remain alive and in remission at 11, 11, and 24 months. Comparison of the survival of patients receiving LDIT with that of an equivalent group (with respect to staging and response to induction chemotherapy) of patients who received induction chemotherapy alone showed no significant difference. In this study, LDIT following conventional induction therapy in patients with chemosensitive tumours did not improve survival.