SUMMARY The Pax gene family consists of nine members encoding nuclear transcription factors. Their temporally and spatially restricted expression pattern during embryogenesis suggests that they may play a key role during embryogenesis. Direct evidence for the important role of the Pax genes during embryonic development has been demonstrated by the correlation of mouse developmental mutants and human syndromes with mutations in some Pax genes. To date three Pax genes have been shown to be mutated in undulated, Splotch and small eye, respectively. In man, Pax-3 is mutated in the Waardenburg syndrome, while in aniridia Pax-6 is mutated.