Friedreich's ataxia (FA) is a progressive degenerative disease involving both central and peripheral nervous system. It is an autosomal recessive hereditary disorder, which begins around puberty and has an unknown genetic basis and biochemical defect. The recent mapping of FA locus in human chromosome 9 by means of the analysis of the molecular genetic linkage has permitted to evaluate FA genetics with polymorphic genetic markers (RFLPs) that are secreted linked with the FA gene. The normal and mutant allele secretion of FA was evaluated in ten Spanish families with one or two members with FA by means of several cloned probes (MCT112, DR47, D9S1 and HHH220), localized in chromosome 9 and strongly linked to FA gene, with the aim of achieving a predictive diagnosis of relatives in the pediatric age and to detect healthy carriers. In 9 out of 10 families some totally or partially informative RFLP were found. In 5 of 6 relatives in pediatric age the future development of the disease could be ruled out. By contrast, the carrier status could only be identified in three relatives. In a family with two affected children a genetic recombinant for D9S1 was found. Remarkably, one of them had a better clinical evolution and preserved tendon reflexes in lower limbs.