Abstract Because the erythrocyte (RBC) in Duchenne's muscular dystrophy (DMD) is thought to be a suitable experimental paradigm for the sarcolemma, the RBC membrane-bound enzyme (Ca 2+ + Mg 2+)-ATPase has been investigated as to its relevance to abnormalities of calcium metabolism in DMD muscle. In this study, RBC (Ca 2+ + Mg 2+)-ATPase activity, intracellular calcium and potassium contents and complete hemogram were examined in 10 DMD patients and 16 age-matched controls. (Ca 2+ + Mg 2+)-ATPase activity was found elevated in the DMD RBC, consistent with reports from previous studies, but no abnormalities in intracellular calcium, potassium or hemograms were detected. It seems that although the (Ca 2+ + Mg 2+)-ATPase activity is changed, it bears no relevance to calcium homeostasis in DMD RBC. It is inferred that the increase in intramuscular calcium in DMD muscle, which is also found in other neuromuscular diseases, may be a non-specific finding in the diseased muscle and part of the final common pathway leading toward cellular degeneration and death.