In patients with advanced bladder cancer receiving chemotherapy, early assessment of response can avoid unnecessary toxicity. The aim of this study was to assess the role of tumour markers in monitoring response. Serum levels of one or more of markers beta human chorionic gonadotrophin (betahCG), carcinoembryomic antigen (CEA), CA125 and CA19.9 were measured in 74 patients with advanced bladder cancer receiving chemotherapy from 1992 to 1997. Forty-three of 74 (58%) of patients had at least one raised marker (1.5 times upper limit of normal range). This was more common in patients with extra-pelvic disease than in those with disease confined to the pelvis (P = 0.002). Thirty-eight of 78 (49%) assessable patients had a radiological response. Neither clinical response (P = 0.81) nor survival (P = 0.16) differed between marker-negative and marker-positive patients. Clinical response was strongly related to marker response in the 35 comparable patients (P = 0.0001). No patient had a clinical response without response of at least one marker. Ninety per cent of patients who achieved a marker response had done so by 8 weeks. Monitoring of tumour markers in patients with advanced bladder cancer can help predict the response to chemotherapy.