C.A.H. due to 21-OH deficiency is an inherited recessive disorder linked to the HLA-B locus on the chromosome 6. In human beings, there are two 21-OH genes (A and B) located near C4 genes in the major histocompatibility complex; the nature of the gene alterations responsible of C.A.H. remains matter for debate. Thus restriction maps, C4 and HLA typings were performed in 14 families with 21-OH deficiency. This report is focused on the analysis of Taql restriction DNA fragments in using 2.7kb murine 21-OH probe including the 3' non-coding region (Amor et al., Proc. Natl. Acad. Sci. USA, 1985, 82, 4453). Four bands were shown : 3.7 and 2.8 kb (gene A), 3.2 and 2.6 kb (gene B). Three series of results were observed : 1) all 4 bands had the same intensity in 9 families in which 2 patients were heterozygous for HLA Bw47. 2) The relative intensity of gene B bands was decreased in patients of 4 families, 2 of which were heterozygous for HLA Bw47; a recombination was demonstrated. 3) Gene A bands were missing in index patient and his mother who were heterozygous for HLA B8, a rare haplotype in this C.A.H. Conclusion: 1) in patients of only 5 out of 14 families Taql restriction maps were modified and a polymorphism cannot be excluded in 2 of them. 2) C.A.Hs with or without salt loss were found in the two first groups selected above and 3) additional analyses are necessary to determine whether each clinical type of 21-OH deficiency is due to a specific 21-OH gene alteration.