PURPOSE: To evaluate the hematologic toxicity of gemcitabine and cisplatin (GC) in patients with advanced transitional cell carcinomas. MATERIALS AND METHODS: From 25 patients, with advanced transitional cell carcinomas, 8 had previously received M-VAC (methotrexate, vinblastine, doxorubicin and cisplatin) chemotherapy for a metastatic disease, and were scheduled to receive gemcitabine, 1,000mg/m2, intravenously, over 30 minutes, on days 1, 8 and 15, and cisplatin, 70mg/m2, over 1 hour, on day 2 of a 28-day cycle. The hematological toxicities of each cycle were evaluated. RESULTS: The main hematological toxicities were thrombocytopenia (grade 3 in 24% and grade 4 in 16% of patients), leukopenia (grade 3 in 14% of patients) and anemia (grade 3 in 12% of patients). Four of the patients that experienced grade 4 thrombocytopenia had a tendency for recurring grade 4 thrombocytopenia during the GC chemotherapy. However, there was no evidence of bleeding. CONCLUSIONS: The most severe hematological toxicity of the GC chemotherapy was thrombocytopenia. The careful observation of the patients that experience grade 4 thrombocytopenia is recommended.