DNAs from unrelated healthy individuals and unrelated individuals affected with 21-hydroxylase deficiency (congenital and late-onset adrenal hyperplasia) were digested with seven restriction enzymes and hybridized with a cDNA probe specific for human 21-hydroxylase genes. Associations were found between restriction fragments and the two forms of the disease: The late onset form is associated with a double dose of a 14 kb fragment generated by EcoRI and with a triple dose of a 3.2 kb fragment generated by Taq I in patients with HLA B14 haplotypes; The classical congenital form is negatively associated with the 14 kb fragment and with a 3.7 kb fragment generated by Taq I in patients with HLA Bw47 haplotypes. A 3.2 kb Taq I fragment is negatively associated with the HLA B8 haplotypes. The other five enzymes tested give no polymorphisms or polymorphisms without correlation with the two forms of the disease.