The nature of the metabolic errors in phytanic acid storage disease and in Niemann-Pick Disease are being studied. The studies on phytanic acid storage disease include the following aspects: 1) Studies on the metabolism of phytanic acid. Recent results show that in lecithin isolated from red blood cells of patients with homozygous form of the disease, phyantic acid is distributed between the one-position and the two-position, more than 85% in the one-position. Comparison of different lipoprotein fractions from an affected patient show approximately equal content of phytanic acid (as percentage of total fatty acids) in very low density, low density, and high density lipoproteins. 2) Studies of variant forms of phytanic acid storage disease. Cell culture studies on a patient with mild but definite clinical symptoms have shown an intermediate rate of phytanic acid oxidation, i.e., comparable to that of heterozygotus patients. Oxidation of intravenously injected phytanic acid-14C will be measured and compared to values in normal subjects. 3) Evaluation of therapy. Several patients on phytanic acid-low diets are being followed with regard to phytanic acid levels and clinical symptoms. Little or no further progress of the disease has occurred. Empirically it has been found that several foodstuffs can be added to the diet without increasing plasma phytanic acid level. Because it has been noted that some patients with Niemann-Pick disease accumulate significant concentrations of bis(monoacyglyceryl) phosphate (BMP), the metabolism of the latter is being studied in normal liver fractions. Phosphatidylglycerol (PG) is then an important precursor of BMP. However, lysosomes do not contain or synthesize PG. Studies are under way on the possible interaction between lysosomes and other cell fractions in the synthesis of BMP. Cell lines from patients with Niemann-Pick disease Type A and Type C are being studied with respect to the biosynthesis of BMP and sphingomyelin.