A new polymorphic DNA marker for the diagnosis of autosomal dominant adult polycystic kidney disease (APKD) has been identified. The new marker, 24-1, flanks the APKD gene on the side opposite to the alpha globin on the short arm of chromosome 16. When both DNA polymorphisms bracketing the gene are informative the reliability of prenatal and presymptom diagnosis of polycystic kidney disease in non-recombinants (92% of cases) is more than 99%.