Oral BOF-A2 (Emitefur), a new derivative of 5-fluorouracil (5-FU) containing both 1-ethoxymethyl-5-FU (EMFU), a masked form of 5-FU, and 3-cyano-2,6-dihydroxypyridine (CNDP), an inhibitor of 5-FU degradation, was administered to 71 non-small cell lung cancer (NSCLC) patients in a multi-center phase II study. The patients were scheduled to receive at least 2 courses of treatment, each consisting of 200 mg twice daily for 2 weeks followed by a 2-week rest period. Out of 62 evaluable patients, 11 (18%) responded (8 of 44 adeno- and 3 of 15 squamous cell carcinomas). Thirty-four patients showed no change and 17 progressive disease. The incidences of grade > or = 2 hematologic toxicity were 5-8% for leukopenia, thrombocytopenia, and anemia. The incidences of non-hematologic toxicity of grade > or = 2, such as anorexia, nausea/vomiting, and diarrhea, were close to 20% or lower.