SUMMARYCareful genotyping of three families, each having a member with classical salt‐losing steroid 21‐hydroxylase deficiency, has allowed identification of carrier haplotypes. Digestion with TaqI or EcoRI and probing with a cDNA probe for the 21‐hydroxylase genes (pC21/3c) revealed that all six affected haplotypes are abnormal with at least EcoRI. The data suggest that there is extreme polymorphism of the 21‐hydroxylase genes and that dysfunction may result from several different abnorm