A randomized trial of combination therapy with bestatin (30 mg daily, every day) was performed in 238 patients with inoperable primary lung cancer from August, 1981 through April, 1984. Of the 238 patients, 227 were evaluable: 113 treated by bestatin combination therapy and 114 controls. There was no statistically significant difference in response rate or survival between the 2 groups. In squamous cell cancer response was observed in 34.5% of the bestatin group and 17.9% of the control group. The analysis, including Cox's proportional hazard model, revealed that the survival tended to be longer in the bestatin group (median survival 40 weeks) than in the control group (median survival 24 weeks; p = 0.051). This suggests that addition of bestatin might be beneficial in squamous cell cancer of the lung but further, more rigidly controlled, clinical trials are necessary before more definitive conclusions can be drawn.