Abstract The concentration of 1.2-diacylglycerol in mitochondria and microsomes of normal human muscle was estimated to be 1.7 ± 0.6 and 9.2 ± 1.9 nmol · mg protein −1, respectively. The molecular species profile of 1.2-diacylglycerol was obtained using high pressure liquid chromatography which yielded 14 fractions. Corresponding studies were carried out for normal and dystrophic muscle. 1. (1) No significant difference could be seen between the 1.2-diacylglycerol patterns in normal muscle mitochondria and in microsomes. 2. (2) There was a radical shift in the 1.2-diacylglycerol pattern in both dystrophic organelles, mainly with a decrease in 16:0/16:0 species. 3. (3) In dystrophic mitochondria the total level of 1.2-diacylglycerol was higher. When examined in the light of results obtained previously, the results support the thesis that there is a defect in sn-glycerol-3-phosphate acylation and phosphatidic acid phosphatase in Duchenne muscular dystrophy, although the variations of the 1.2-diacylglycerol content and pattern in dystrophic mitochondria were unexpected.