Troxacitabine. a promising new L-nucleoside, inhibits DNA polymerase and leads to complete DNA chain termination. The National Cancer Institute of Canada Clinical Trials Group (NCIC-CTG) conducted a phase II study to assess the efficacy and toxicity of troxacitabine in untreated patients with advanced non-small-cell lung cancer (NSCLC). Previously untreated patients were eligible if they had inoperable stage IIIB or IV NSCLC, ECOG PS < or = 2, adequate hematology and biochemistry, and at least one bidimensionally measurable lesion. Patients with prior malignancy or brain metastases were excluded. Troxacitabine (10 mg/m(2)) was administered intravenously over 30 minutes every 3 weeks. Between June 1999 and May 2000, 17 eligible patients received treatment. Patient characteristics included: median age 64 years; female 41%; stage IV (94%); PS 0 (12%), 1 (59%), and 2 (29 %), 3 or more disease sites (59%). In 17 patients, there were 8 stable disease, 9 disease progression, and no objective responses. Median duration of stable disease was 3.6 months (range = 2.0-7.1). A total of 56 cycles were administered (median = 3), and 88% of patients received 90% or more of the planned dose intensity. The majority (82%) of patients experienced skin rash. Hematologic and biochemical toxicities, grade 3/4 (%) were: granulocytopenia (41), anemia (12), thrombocytopenia (6), and hyperglycemia (6). Troxacitabine appears to have little activity in NSCLC in the dose and schedule tested.