Some recently described abnormalities in the serum and red cell membranes in Duchenne dystrophy have been examined as methods of carrier detection in a single-blind controlled study. Twelve carriers (4 definite, 3 probable and 5 possible carriers previously found to have raised creatine kinase levels) and 12 normal female controls of the same age, were examined on 3 separate occasions at approximately two-weekly intervals. Analysis of age-dependent red cell shape changes, serum haemopexin levels, red cell K+ efflux rate, sensitivity of red cell ghost membrane ATPase to ouabain, membrane protein phosphorylation studies and lactate dehydrogenase isoenzyme profiles on agarose gel electrophoresis all failed to distinguish carriers from controls. The carriers suffered muscle cramps more frequently than the controls and all but one carrier and two control subjects were correctly identified by manual muscle strength testing, certain proximal muscles in particular being consistently weaker in carriers than in the control group subjects. Scalar electrocardiography revealed higher values for the R/S ratio in Leads V1 and V2 and the sum (R-S) in V2.