The 14 exons of the PAX6 gene have been analysed exon-by-exon using SSCP in 6 aniridia families. In each family band shifts were observed on the SSCP gels for only one exon and direct PCR-sequencing revealed mutations in each case. Two mutations involved C-->T transitions in CGAarg codons in exons 9 and 11. Another C-->T transition converted a CAG-glutamine to a TAG-stop in exon 7. Small insertions created frameshifts which produced downstream stop codons in another two patients and an A-->T mutation disrupted the splice donor site of exon 5 in the remaining family. Thus, complete inactivation of the PAX6 gene is predicted in all cases. Analysis of other affected members of the families showed that, in each case, all affected individuals carried the same family-specific mutation. One polymorphism was found in exon 7. This data strongly supports the candidature of PAX6 as the gene responsible for hereditary aniridia.