Serum, urine and tissue levels of b-hCG (beta subunit of human chorionic gonadotropin) were determined in 30 patients with transitional cell carcinoma (TCC) of the bladder and 10 controls. Serum b-hCG levels were significantly higher than controls in all tumour groups (p<0.05), while no significant difference between the grade groups was observed (p>0.05). The urine b-hOG grades which appeared at higher levels than controls in grade I and Il tumours (p<0.05), but lacking any significant difference between the grade Ill tumour group and controls (p>0.05). The tissue b-hCG levels were raised as the tumour grades increased, significant differences existed among grade I, II and Ill tumours, and between the controls and the latter two grade groups (p<0.05, for each). Beta-hCG seems promising as a tumour marker for TCCs of the bladder, but prospective long-term trials remain to be conducted to assess its prognotic value.