The authors have studied through histochemical methods the onset of lipids, cholesterol and $3\beta$-hydroxysteroid dehydrogenase ($3\beta$-HSDH) in the interrenal and the genital ridges of Lacerta sicula embryos. Lipids and cholesterol are already recognizable in the interrenal cells at the stage of 10-11 mm of total length, whilst $3\beta$-HSDH appears at the stage of 12-13 mm. In the genital ridges rare sudanophilic droplets are already present at the stage of 10-11 mm in the cortical and medullary cells. The Schultz test and the reaction for $3\beta$-HSDH are positive in the medullary cells of the ovary and the somatic cells of the seminifereous tubules of the testis (Sertoli's cells ?) from the of 16-17 mm, after the onset of sex differentiation. In the adult testis the enzyme as well as lipids and cholesterol are located only in the interstitial cells. The onset of steroid biosynthesis in the gonads after the stage of sex differentiation further confirms the hypothesis that the «embrionic sex inductors» are different from sex hormones of the adults.