Recovery of speech after infarction of the left pars opercularis (POp) may be due to recruitment of homotopic cortex in the right hemisphere. Using positron emission tomography, we investigated activity within left and right POp during everyday propositional speech. We studied seven aphasic patients with left anterior perisylvian infarction which included the POp. We compared their data with two control groups: 12 normal subjects and 7 anterior aphasic patients whose infarcts spared the left POp. During propositional speech, normal subjects activated the left POp, left posterior perisylvian cortex, and a distributed, predominantly left-lateralized, extrasylvian neural network. Importantly, activity in the right POp was reduced relative to a baseline nonspeech condition. In patients with infarction of the left POp, activity in the right POp was reversed: speech activated the right POp above baseline. Patient controls activated the left POp but did not show the normal relative reduction in activity in the right POp. In both patient groups, posterior perisylvian and extrasylvian activations remained unchanged from normal. This result demonstrates that infarction of the left POp is associated with a chronic change in function of the contralateral homotopic cortex during speech.