Cultured amniotic fluid cells from two mucolipidosis type IV (MLIV)-affected fetuses demonstrated accumulation of phospholipids and gangliosides when compared with normal controls. Like cultured skin fibroblasts from MLIV patients, cultured amniotic cells from the affected fetuses accumulated primarily lyso phospholipids and this could be demonstrated by radioactive labelling with appropriate precursors, either inorganic phosphate or oleic acid. Furthermore, like cultured skin fibroblasts, there was significant retention of exogenously supplied GD1A ganglioside in the affected amniotic cells. This storage was previously demonstrated to be unique to MLIV and thus can be used at present as a specific procedure for prenatal diagnosis of MLIV.