A late phase II study of LY188011 (gemcitabine hydrochloride), a new synthetic anticancer agent, was conducted at 20 Japanese institutions to evaluate the efficacy and safety of the agent administered alone in patients previously untreated with chemotherapy for primary non-small-cell lung cancer (NSCLC). All of the total 73 patients enrolled were eligible and 69 completed at least one course of LY188011 therapy. All patients were evaluated for safety. The response rate was 26.0% (19/73) of eligible patients. The most common adverse reactions included decreased hemoglobin, leukopenia, neutropenia, anorexia, nausea/vomiting, and malaise. Most adverse reactions were of grade 1 or 2 and only a few grade 3 or 4 reactions were reported. However, since a death occurred due to interstitial pneumonia, careful observation for this event is needed. Based on these results, it may be concluded that LY188011, a new anticancer agent, has adequate efficacy for the treatment of NSCLC and causes few clinically relevant adverse reactions.