We evaluated 39 patients with various stages of bladder carcinoma to determine alterations in monocyte function. Since the monocyte plays an important role in the effector arm of the immune system defective function may explain the host's inability to destroy neoplastic cells. As a group these 39 patients demonstrated defective monocyte monocyte function. There was no correlation between tumor stage and degree of chemotactic defect. Patients with invasive carcinoma had a significant return of monocyte chemotactic response toward normal postoperatively (p less than 0.005). Monocyte function was improved also in 3 patients who received Bacillus Calmette-Guerin immunotherapy (p less than 0.05).