The study describes lectin reactivity of the developing vascular network in fetal mammalian skin. Skin samples were taken from fetuses of different gestational age of the pig, the goat and the cat. Clearly positive, endothelial lectin staining of capillaries and smaller vessels could only be obtained during mid gestation. The sequence of lectin reactivity, demonstrating: 1st alpha-D-N-acetylglucosamine and N-acetyl-alpha-D-galactosamine, 2nd alpha-D-galactose and sialic acid, and 3rd alpha-L-fucose, sialic acid and probably alpha-D-mannose/alpha-D-glucose residues, emphasizes different stages of cell surface coat as well as of cell membrane development. Thus, the typical outgrowth period of developing integumental blood vessels is reflected histochemically.