After a 26% response rate was reported with a 20/mg/m2/week vinorelbine (VRL) dose, a multicenter phase II trial of a modified weekly VRL treatment protocol (30 mg/m2 days 1 and 8 every 21 days) for unresectable non-small cell lung cancer (NSCLC) was designed to determine its clinical activity, toxicity, and survival of treated patients. As myelotoxicity frequently precludes the administration of VRL, by suppressing the dose that would correspond to day 15 of a weekly protocol, we allowed bone marrow recovery to take place and avoided the administration of the drug at the nadir of the cycle. The trial included 71 consecutive, previously untreated patients with unresectable and measurable disease. A total of 297 three-week treatment courses were administered with an average of 4 courses per patient (range 1-11). Results showed that in spite of attaining a median dose intensity of 19 mg/m2/week, this modified weekly VRL treatment regimen has a low level of activity (7.5% response rate) in NSCLC. Although a more tolerable level of toxicity is achieved, in order to maintain its antitumor activity, the recommended dose of VRL when given alone for NSCLC treatment (30 mg/m2/weekly) should not be decreased.