Neutral lipid storage disease with ichthyosis is a newly recognized heritable disorder characterized by widespread cellular triglyceride storage. Lipid metabolism in fibroblasts cultured from three affected family members was studied. The stored lipid is triglyceride composed of an unremarkable fatty acid profile and derived from both exogenously-supplied and endogenously-synthesized fatty acids. Lipid storage could not be corrected by prolonged culture in lipid-depleted media. Acetyl CoA carboxylase activity and beta-oxidation of palmitate were both normal. Taken together, these studies exclude a primary defect of fatty acid uptake, over-synthesis or impaired beta-oxidation. Moreover, triacylglycerol lipase activity of homogenates of fibroblasts from patients with NLSDI examined over the range of pH 3.5-8.5 was normal.