The pattern of secretion of human chorionic gonadotrophin (hCG) and its subunits in male subjects with tumours of the genital tract was examined by gel filtration, radioimmunoassay, immunoradiometric assay, bioassay and binding to Concanavalin A. The predominant form of hCG was the intact molecule but all patients had increased levels of free beta subunit. The intact hCG was active in a mouse Leydig cell bioassay and was normally glycosylated. High concentrations of free alpha subunit were not found and the ratio of alpha subunit: beta subunit was less than that in normal pregnancy. It is concluded that hCG-secreting tumours of the male genital tract are similar to choriocarcinoma in the female in that large quantities of intact hormone are produced with a disproportionate increase in free beta sub-unit.