Immunoglobulin A (IgA) levels in semen and in prostatic fluid of 48 patients with benign and malignant diseases of the prostate were estimated. It is speculated from this small study that the IgA levels rise in benign prostatic hyperplasia; in early adenocarcinoma of the prostate (Stages A and B) the rise if furthered, while in the late stages (Stages C and D) the levels fall.