Elsamitrucin (BMY-28090) a novel fermentation product has demonstrated pre-clinical anti-tumour activity against a number of cell lines. The dose limiting toxicity in phase I studies was a reversible increase in hepatic transaminase. This study was initiated to determine the activity of elsamitrucin in patients with previously untreated, bi-dimensionally measurable, cytologically or histologically proven, non-small cell lung cancer who were not curable by surgery. Elsamitrucin at a dose of 25 mg/m2 was administered intravenously over 5-10 min weekly for a minimum of 6 weeks. Seventeen patients were entered on study, 15 were evaluable for toxicity and 14 evaluable for response. No responses were documented in the 14 patients evaluable for response. Both hematological and non-hematological toxicities were mild to moderate in severity. The commonest being nausea, vomiting, lethargy and local skin reactions at the site of the infusion. These results indicate that elsamitrucin when given in this dose and schedule to patients with surgically incurable non-small cell lung cancer has no activity.