Reitnoic acid (RA) is known to be tetratogenic in mammals causing a range of defects including abnormalities in craniofacial development. To investigate the effect of RA during organogenesis, in situ hybridization with digoxigenin labeled probe was used to study the localization of RAR-βtranscripts in the rat embryos from day 10.5 to day 12.5 of development. Day 10.5 old rat embryos were exposed to all trans-reitnoic acid for the culture period (48hrs). Embryonic growth was retarded at any concentration of RA. Hypoplasia of branchial arches and short limb bud occurred commonly. RAR-βtranscripts were distributed in anterior facial mesenchyme, branchial arches, otic area, mesonephros and neuroepithelial lining cells. Distribution in vitro was not different from that of in vivo. These results leave open the possibility that RAR-β is involved in mediating the effects of applied reitnoic acid upon facial development. The level of expression was shown in the group treated with 30μg/ml most extensively and was reduced in the group of 3μg/ml, vehicle control and non-treated control gradually. Clear changes in the expression of RAR-β were detectable after RA treatment in a dose-dependent manner.