OBJECTIVE In an analysis of enzymes in easily accessible tissues like blood cells, serum can provide a valuable information and a simple tool for disease and carrier detection. In the study presented we have analyzed calcineurin activity in Duchenne muscular dystrophy (DMD) and carrier sera and lymphocytes for its diagnostic value and its status in DMD pathology. METHODS We have monitored calcineurin activity in sera and lymphocytes of DMD, in carriers and in controls using colorimetric method by following the p-nitrophenol released in the presence and absence of Trifluoperazine (TFP), an inhibitor of calcineurin. RESULTS Results showed a significant decrease in serum and lymphocyte calcineurin activity in DMD (p<0.001) without alteration in carriers compared to normal. CONCLUSIONS Further studies are required to understand possible alterations mediated by calcineurin with reference to DMD lymphocytes as any alteration in phosphorylation/dephosphorylation pathway can disturb the normal functioning of these cells. The decreased calcineurin activity observed in DMD serum compared with controls could be further examined for its diagnostic utility.