Glycerol 3-phosphate is an initial metabolite in the biosynthesis of phosphoglycerides and triacylglycerols. Both glycerol and glucose are precursors of glycerol 3-phosphate. Cultured skin fibroblasts from patients with glycerol kinase deficiency utilized glucose, but not glycerol in the biosynthesis of phosphoglycerides and triacylglycerols. Phosphoglyceride and triacylglycerol biosynthesis in glycerol kinase deficiency fibroblasts is not diminished by the inability to use glycerol as a precursor of glycerol 3-phosphate.