Cultured amniotic-fluid cells from a fetus at risk for homozygous familial hypercholesterolaemia (F.H.) almost completely lacked cell-surface receptors for plasma low-density lipoprotein (L.D.L.), as evidenced by direct measurement of binding, uptake, and degradation of 125I-L.D.L.Functional consequences of L.D.L. binding to the receptor--i.e., suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase and stimulation of cholesterol esterification--were proportionately reduced when compared with results in cultured amniotic cells from two control fetuses.