Hitherto, mutations that lead to autosomal dominant adult-type polycystic kidney disease have been found to be linked to the alpha-globin genes on the short arm of chromosome 16. In an Italian family, absence of linkage between the disease mutation and alpha-globin indicates that the condition can be caused by mutations in a second gene. The clinical features of the disease in this Italian family are indistinguishable from those found in the "linked" families. The finding that there are two polycystic kidney disease genes means that linkage must be demonstrated independently in each family before predictive tests with DNA probes can be used reliably.