Electrocardiographic (ECG) abnormalities characteristic of Duchenne muscular dystrophy (tall R waves in the right precordial leads and deep Q waves in the lateral chest leads) are rarely observed in carriers, but Emery (1969) found that the (R-S) amplitude sum in lead V1 was significantly greater in carriers than in age-matched controls. In a prospective single-blind study, we analyzed coded records from 11 carriers and 12 age-matched normal women for (R-S) amplitude sums and R/S ratios in leads V1 and V2. Values in carriers were significantly greater for all these characteristics, discrimination being most marked for R/S in V2 (p less than 0.01). This was confirmed in a further retrospective study, comparing records from 18 carriers with 100 normal ECGs from women of the same age range. Density functions for (R-S) in V1 and the R/S ratio in V2 derived from carrier and normal population can be incorporated into probability calculations to determine risk of carrier status.