A combination of docetaxel (D) and cisplatin (P) is one of the standard regimens for the initial treatment of advanced non-small cell lung cancer (NSCLC). Yet, the toxicity of D administered at 75 mg/m(2) in three weekly doses to patients is a concern. The aim of this study was to assess the efficacy of a lower combination dose, 60 mg/m(2) of D and 60 mg/m(2) of cisplatin (P), as a treatment for NSCLC. In this randomized, phase III trial, we compared the response rates (RRs) and toxicity profiles of two combination regimens, D/P 75/60 vs. 60/60 mg/m(2), to patients with stage IIIB or IV NSCLC. A total of 132 patients were randomized to the 75/60 (n=65) or 60/60 (n=67) dosage group. Non-inferiority of 60/60 group compared to the 75/60 group was confirmed by the RR (38.5% for the 75/60 group and 40.3% for the 60/60 group, 95% confidence interval -14.8 to 18.5, meeting the predefined non-inferiority criterion). The dose reduction rate and incidence of grade 3-4 neutropenia were significantly higher in the 75/60 group. The incidence of neutropenia was significantly higher in those with the non-expressing genotype (GG) compared to the AG or AA genotypes of CYP3A5. We determined that DP 60/60 was not inferior to DP 75/60 in RR, and that the reduced combination dosage provides a better safety profile for patients.