The authors describe a method for the radioimmunoassay of 17 alpha-hydroxyprogesterone in the saliva. The limit of detection is 1.96 fmole/tube. Salivary 17 alpha-hydroxyprogesterone was measured in control subjects. Values found were of 296 +/- 115 pmol/l in the male, and 251 +/- 23 pmol/l in the female during the follicular phase and 401 +/- 94 pmol/l during the luteal phase, and 115 +/- 30 pmol/l in the prepubertal child. Concentrations were much higher in the newborn and decreased during the first days of life. Variations in salivary concentrations were compared with those in plasma 17 alpha-hydroxyprogesterone during the 24-hour period and with the Synacthene stimulation test. The excellent correlation (r = 0.0969) between salivary 17 alpha-hydroxyprogesterone and plasma 17 alpha-hydroxyprogesterone in 28 patients being treated for 21 hydroxylase deficiency makes it possible to suggest salivary assay in place of plasma assay in the therapeutic follow-up of such patients.