We describe a method for the isolation and functional characterization of insulin receptors from chorionic villi and cultured amniotic fluid cells. The functionality of these receptors is assayed by measuring the insulin-induced stimulation of autophosphorylation of the receptor beta-chain. The method is expected to allow the prenatal diagnosis of those forms of leprechaunism and related diseases which are the result of a decreased stimulation by insulin of receptor autophosphorylation. A pregnancy at risk for leprechaunism was examined and an unaffected child was correctly predicted by study of the functionality of the insulin receptor on cultured amniocytes and by echoscopic examination.