By a general survey in the hopitals of northeast Italy, Duchenne cases have been located and identified over a 20-year period. In a more restricted area screening for Duchenne carriers has been carried out in affected families. This procedure made possible an exact estimate of the incidence rate, prevalence rate, and mutation rate in a large sample of population. Prevalence rate was found to be 34x10(-6), incidence rate about 28x10(-5), while mutation rate was found lower than 50x10(-6) by the direct method. The discrepancy between the results obtained by the Haldane formula and those obtained by the direct method for the estimate of the mutation rate is discussed.