PAX-genes encode important transcriptional factors during embryogenesis. They are also involved in human diseases, Waardenburg syndrome, Aniridia and tumors. We report in the present paper a preliminary in situ hybridization study of PAX3-, PAX5- and PAX6-gene expression during human embryonic development. PAX3-gene is expressed in the neural groove before closure, and in the closed neural tube. Afterwards, its expression is observed in the mesencephalon, the rhombencephalon and the spinal cord. PAX5-gene expression is restricted to the mesencephalon-rhombencephalon boundary and the spinal cord. PAX6-gene is expressed early in the neural tube, just after its closure. Afterwards, its expression is observed in the forebrain, the rhombencephalon, the somites and the spinal cord. These patterns of expression are observed early during human embryonic development and are specific in time and space. This preliminary report shows the feasibility of in situ hybridization methodology for studying the expression of developmental genes during the early stages of human embryogenesis. It opens the way to study the pathogenesis of polymalformative syndromes and tumorigenesis.