The scanning ultrastructural examination of a series of 31 hydatidiform mole and 12 healthy placental specimens of similar gestational age has revealed a variety of surface architectures more common in molar tissue. Characteristic paddle-shaped sprouts, ridging of the syncytial maternal oriented surface and microgibbosities are described. These structures are explicable in terms of organellar hyperplasia of cortical cytoskeletal elements found in healthy tissue. Specific morphological evidence of involvement of these elements in a condition where aberrant growth control leads to the characteristic trophoblastic hyperplasia is a further indication that cytoskeletal elements may mediate transformation. An increase in resolution obtained over previous scanning electron microscope studies has allowed the description of detailed features such as 'caveolar collars' on the maternal oriented healthy and molar trophoblast surfaces. These observations are of relevance to understanding the mechanisms of several cell physiological processes, including transepithelial transport. New observations of a reticular organization in the surface layer of molar trophoblast indicate that a syncytioskeletal layer, with organization resembling that previously described in healthy chorionic villi, is also present in molar villi.