Phospholipid incorporation of 32P by primary myotube cultures and the tissue activity of sarcolemmal Na+/K+-transporting ATPase were studied to determine whether the absence of dystrophin from dystrophic (mdx) muscle would affect membrane lipid synthesis and membrane function. The incorporation of 32P by phospholipid as a ratio with total protein was greater in cultured dystrophic cells compared with control cells. The mdx cells also incorporated more 32P than control cells into phosphatidylethanolamine, which is thought to increase prior to myoblast fusion, and less into phosphatidylserine, phosphatidylinositol, and lysophosphatidylchoiine. There was no difference in total protein content or [3H]leucine or 32P incorporation into the aqueous fraction of dystrophic and control cells, although dystrophic cells incorporated less [35S]methionine into protein than controls. Isolated sarcolemma from mdx skeletal muscle tissue demonstrated a consistently greater specific activity of ouabain-sensitive Na+/K+-transporting ATPase than sarcolemmal preparations from control skeletal muscle. These observations suggest that cytoskeletal changes such as dystrophin deficiency may alter the differentiation of membrane composition and function.Key words: muscular dystrophy, mdx, myogenesis, sarcolemma, ouabain-sensitive ATPase, phospholipid.