18,000 newborn males were screened for Duchenne muscular dystrophy (DMD) by creatine kinase (CK) analysis of filter paper blood spots between Jan 1, 1986, and Dec 31, 1987. 5 affected boys have been identified, and in 3 of 5 probands molecular deletions or duplications have been found. 3 of 5 mothers were judged highly likely to be carriers of DMD because of repeatedly raised CK levels, identified gene rearrangements, or both abnormalities. 1 mother has a very low probability of being a carrier and 1 is at an intermediate risk. The use of DNA analyses in new DMD probands identified by neonatal screening has allowed confirmation of the diagnosis and accurate assignment of carrier status in mothers and female relatives in over half the cases studied, and may help to reduce the population incidence of DMD by avoiding delay before clinical diagnosis.