A histochemical study of lectin binding was performed to assess staining with lectins and, therefore, the expression of complex carbohydrates in human neoplastic urothelium. Forty-seven patients with transitional cell carcinoma of the bladder and six controls were studied. Cryostat sections were stained with a panel of 10 biotinylated lectins by means of the avidin-biotin-peroxidase technique. Sixteen tumours were also studied after conventional formalin fixation and paraffin embedding. In general, staining by lectins of tumours was more intense than staining of control urothelium and staining of tumours invading bladder muscle was greater than that of superficial tumours (both P less than 0.001). A small but statistically significant diminution of staining was observed after formalin fixation and paraffin embedding (P less than 0.05). Four lectins--Bandeiraea simplicifolia (P less than 0.01), Vicia villosa (P less than 0.01), peanut agglutinin (P less than 0.001) and soyabean agglutinin (P less than 0.001) stained invasive tumours more frequently than superficial tumours in frozen sections. Thus, increased binding of certain lectins was found in human transitional cell tumours and correlated with muscle invasion and poor differentiation.