Carboplatin (JM8) and etoposide (VP16) have demonstrated activity against a range of solid tumours. A retrospective study has looked for evidence of enhanced radiation pneumonitis when these drugs are employed in conjunction with irradiation. Twenty-nine patients with limited disease small cell lung cancer (S.C.L.C.) received JM8 (300 mg/m2) and VP16 (300 mg/m2) at intervals of 3-4 weeks for 4 cycles followed by thoracic irradiation. Twenty-one were evaluated and compared with 21 matched non-S.C.L.C. patients treated by radiotherapy alone. Patients were stratified into three groups according to the radiation dose schedule normalised using Wara's modification of Ellis' formula (n = 0.38, t = 0.06) [28]. Group 1 received less than 1014 rets, Group 2 1015-1250 rets and Group 3 greater than 1250 rets. Radiological pneumonitis was observed in 57% (12/21) of patients receiving combined modality treatment compared to 71% (15/21) of patients receiving radiation alone with evidence of a radiation dose-response relationship for the appearance of pneumonitis in both groups of patients (p greater than 0.1). In conclusion, no enhancement of radiation pneumonitis by carboplatin (JM8) or etoposide (VP16) has been observed.