In this phase II study, the efficacy and tolerability of gemcitabine were studied in 42 patients with locally advanced or metastatic breast cancer who had received up to one prior chemotherapy regimen in an adjuvant setting. Ten patients had received adjuvant chemotherapy. Twenty-eight patients (67%) had visceral disease spread at entry. Gemcitabine (1000 mg/m2) was administered weekly on days 1, 8 and 15 of a 28-day cycle. The mean number of completed cycles was 3.9 and the mean dose delivered was 942.2 mg/m2. Ninety-seven percent of injections were administered as assigned. No complete responses were observed, but there were six partial responses and 24 patients with stable disease lasting 2-9 months. The overall response rate was 14.3% (95% CI 5.4-28.5%). The median survival for all patients was 15.2 months. Maximum WHO grade 3 and 4 toxicities were observed in five patients for nausea and vomiting, one patient for diarrhea, one patient for pain, seven patients for alanine transaminase, and eight patients for segmented neutrophils. There were no grade 3 and 4 toxicities for alopecia. These data confirm modest single-agent gemcitabine activity in advanced or metastatic breast cancer. Gemcitabine's favorable toxicity profile makes it an ideal candidate for combination chemotherapy.