Developmental dysphasia, a severe childhood learning disorder, is thought to result from problems in hemispheric specialization involving both left and right cerebral hemispheres. Regional cerebral blood flow (rCBF) was measured at rest and during stimulation of both hemispheres independently: dichotic listening for the left, dichaptic palpation for the right. Eight right-handed boys with expressive dysphasia, aged 8 to 12 years, were investigated using SPECT and compared with eight right-handed age-matched boys with Duchenne muscular dystrophy with reading disorders but normal speech. rCBF values at rest were also compared with those of five right-handed age-matched normal boys. In the dichotic task, children with dysphasia differed from children with dystrophia by failure to increase rCBF in the left hemisphere, in Broca's area, but rCBF increased in the right hemisphere, in the region homologous to Broca's area. In the dichaptic task, rCBF increased bilaterally for children with dysphasia whereas in children with dystrophia rCBF increased only in the right hemisphere. At rest the physiological asymmetry was reversed in favor of the right hemisphere in all areas except Broca's area. Surprisingly, the same applied at rest and for all areas in children with dystrophia. These results confirm that functional specialization of both hemispheres is impaired in developmental dysphasia. Moreover, they suggest that learning disabilities associated with Duchenne muscular dystrophy could also be related to abnormal hemispheric specialization.