An enzyme immunoassay for the quantitative measurement of 17-Alpha-OH progesterone (17-Alpha-OHP) in serum or plasma (EDTA-, heparin- or citrate plasma). The steroid 17-Alpha-Hydroxyprogesterone (17-Alpha-OHP) is produced by both the adrenal cortex and gonads. Even though 17-Alpha-OHP has relatively little progestational activity, it is of intense clinical interest because it is the immediate precursor to 11-desoxycortisol (Cpd-S). Because Cpd-S is produced by 21-hydroxylation of 17-Alpha-OHP, measurement of 17-Alpha-OHP is a useful indirect indicator of 21-hydroxylase activity. In congenital 21-hydroxylase deficiency, the most common variety of congenital adrenal hyperplasia (CAH), 17-Alpha-OHP is secreted in abundant excess. It is moderately elevated in the 11-Beta-hydroxylase deficiency as well. Measurement of 17-Alpha-OHP is therefore valuable in the initial diagnosis of CAH. The DRG 17-OH Progesterone ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA), based on the principle of competitive binding. The microtiter wells are coated with a polyclonal [rabbit] antibody directed towards an antigenic site of the 17-Alpha-OHP molecule. Endogenous 17-Alpha-OHP of a sample competes with a 17-Alpha-OHP-horseradish peroxidase conjugate for binding to the coated antibody. After incubation the unbound conjugate is washed off. The amount of bound peroxidase conjugate is inversely proportional to the concentration of 17-Alpha-OHP in the sample. After addition of the substrate solution, the intensity of color developed is inversely proportional to the concentration of 17-Alpha-OHP in the sample.