The activities of serum and urinary alpha-esterases were studied in 49 bilharzial bladder cancer patients, 92 bilharzial patients with other, different, urologic diseases and 22 normal healthy controls. Among the group studied, the bilharzial bladder cancer patients showed the highest level of urinary-alpha-esterases and the lowest ratio of serum/urine activity. These patients showed a significant increase in the activity of urinary alpha-esterases as compared with the normal controls or with the other different bilharzial groups. Although a small but significant increase in serum activity was observed in all the bilharzial groups studied compared with the normal healthy controls, no significant difference was found between the bilharzial bladder cancer patients and the other different bilharzial groups. Biochemical determination of urinary alpha-esterases for bilharzial patients revealed a high degree of accuracy for the diagnosis of bilharzial bladder cancer (95.9%), with low falsely positive (3.26%) and falsely negative (4.08%) results. The activity of urinary alpha-esterases in recommended as a screening test for bilharzial bladder cancer.