PURPOSE: This Phase II trial was designed to determine the response rate, survival, failure-free survival, and toxicity of second-line therapy with karenitecin in patients with relapsed or refractory non-small cell lung cancer (NSCLC). METHODS: Eligibility criteria included: only one prior chemotherapy program, measurable disease, performance status 0-1, adequate hematologic, renal, and hepatic function. Cases were stratified as relapsed or refractory. RESULTS: Fifty-five patients were accrued and 52 were eligible of whom 28 had relapsed and 24 had refractory disease. Overall patient characteristics were: median age 63 years (range, 45-79 years), 52% males, 63% performance status 1, 50% adenocarcinoma, 21% squamous, 15% large cell, and 12% undifferentiated NSCLC. In both strata, one patient each (4%) had a partial response and 12 patients each (43% for relapsed, 50% for refractory) had stable disease. Median survival was 10.4 months (95% CI, 8.5-17.0) for relapsed NSCLC and 6.0 months (95% CI, 3.7-9.7) for refractory NSCLC. One-year survival was 36% (95% CI, 14-58%) and 21% (95% CI, 5-37%) for relapsed and refractory NSCLC, respectively. Frequent toxicities were neutropenia (grade 3/4 in 15/15%) and thrombocytopenia (grade 3/4 in 17/8%). No patient had lethal toxicity. CONCLUSION: Second-line treatment with karenitecin was tolerable with reversible bone marrow suppression as the major toxicity. The partial response rates, median survival times, and 1-year survival rates in the relapsed and refractory subgroups are comparable to overall second-line outcomes for other agents considered active in this clinical setting.