To evaluate beta-catenin expression in human tooth germ development.Specimens of 7 human fetuses aged between the ninth and sixteenth week were examined for beta-catenin expression by immunohistochemistry.In the bud stage, we observed catenin membranous positivity for all primitive dental lamina and dental ridge cells, cytoplasmic positivity for tooth bud and intense nuclear positivity for early-condensed dental mesenchyme. The cap stage was marked by intense cytoplasmic and nuclear positivity in the outer and inner enamel epithelium and the dental papilla and by moderate cytoplasmic positivity in the enamel knot. In the early bell stage, we noted strong cytoplasmic and nuclear staining in the inner and outer enamel epithelium, only moderate membranous and cytoplasmic staining in the stellate reticulum, a high percentage of intense nuclear positivity in the dental papilla and strong focal nuclear and cytoplasmic positivity in the dental sac.All areas with close contact between epithelial structures and ectomesenchymal cells showed increased expression of delocalized cytoplasmic and nuclear beta-catenin. Nuclear localization, tissue expression pattern and timing suggest a pivotal role for beta-catenin in the transcriptional activation of genes probably involved in the mesenchyme-epithelial interactions on which human tooth development is based.