Human Recombinant Granulocyte Colony Stimulating Factor (G-CSF) allows rapid neutrophil recovery after chemotherapy-induced leukopenia. In a prospective series of 54 patients with extensive small cell lung cancer, we evaluated the feasibility and efficacy of accelerated delivery of the AVI chemotherapy regimen. Treatment consisted of Doxorubicin 50 mg/m2 day 1, Etoposide 120 mg/m2 day 1-3 and Ifosfamide 2 g/m2 (+ Mesna 4 g) day 1 and 2 given every 2 weeks and followed by G-CSF (Neupogen, Amgen Roche 5 micrograms/kg/day s.c. day 4-14). Twenty-seven (50%) patients could not receive the total of six courses, seven because of severe septic complication, 10 because of Grade 4 thrombopenia, seven because of non-response and three because of patient refusal. Chemotherapy had to be delayed in 58 out of the 244 administered courses and this was due to thrombopenia in 48% of cases. The probability of optimal dose-on-time administration was 64% at three courses. The mean actually received dose intensity was 93% at six courses (27 patients treated). It was increased by 76% compared to our previously published conventional 3-week interval chemotherapy. The median neutrophil nadirs were stable during the successive treatment courses while haemoglobin and platelet values significantly worsened from cycle 1 to cycle 6. The overall response rate after three courses was 77% in the 48 evaluable patients. The median survival is 8 months overall and 5 months disease free. The actuarial survival is 22% at 2 years. We conclude that substantial dose intensification with accelerated chemotherapy and G-CSF support is feasible. However, the rate of severe infectious episodes is too high and thrombopenia is the main limiting factor. Either growth factors active on the megacaryocytic lineage or haematological rescue with peripheral blood stem cells might be useful in this setting.