Choroideremia is a sex-linked chorioretinal disorder that causes blindness in affected males. The gene for choroideremia has recently been localized by means of recombinant DNA technology to a region of the X chromosome, Xq13-22. We have used two DNA probes, both specific for this region, to study three affected families. The results of linkage analysis of restriction fragment-length polymorphisms (RFLPs) revealed by these probes suggest that in the three families the gene for choroideremia may not be as closely linked to the region of the X chromosome as was previously reported. The estimated degree of linkage between an informative RFLP and the disorder should be considered before predictive testing is offered to people at risk in affected families.