The fatty acid composition of green and white leaf tissue in Acer negundo, Zea mais, and Ilex aquifolium, of green and yellow tissue in Ligustrum ovatifolium and of etiolated and green tissue in Vicia faba has been determined. The mesophytic green leaves examined show a general similarity in fatty acid composition, characterized by a high concentration of non-conjugated octadecatrienoic acid. Chloroplasts were isolated from Vicia and Acer and contain an even higher concentration of this acid and only traces of non-conjugated octadecadienoic acid. Conjugated diene and triene acids occur in traces in chioroplasts, but are also found in non-green leaf tissue. The fats of non-green leaves are in general more saturated than those from green tissue but vary considerably in composition. The relationship between fat composition and plastid development is discussed.