The study was conducted to reveal the effect of retinoic acid (RA) on the developing embryonic organs in which the epithelia come to contact with mesenchyme in mice foetii during pregnancy at the onset of organogenesis. Histogenesis and the expression of TGFβ2 as a potent cell cytokine differentiator were evaluated in skin; lung, kidney and testis at 14, 18 days of gestation. A thinner skin with retarded hair follicles, thin alveolar septa of the lung, retarded differentiation of kidney tubules and deformed Sertoli cells of the developing testicular tubules were noted in retinoic acid-exposed embryos. Depressed fluorescence and PAS content in either the epithelia or the mesenchyme of the tissues under investigation were also noted. These alterations in the different organs were concomitant with decreased expression of TGFβ2 which indicates its importance in proper development and differentiation. From the other hand, the study concluded that successive exposure to retinoic acid at low level during pregnancy suppresses the trans-differentiation of the mesenchyme to epithelia in the organs under investigation through dowenregulation of TGFβ2 expression.