We studied 20 patients aged 46-69 years (mean 57 years) undergoing long-term haemodialysis (HD) and 20 age- and sex-matched controls with single photon emission tomography (SPET) and 99Tcm-hexamethyl-propyleneamine-oxime to look for regional abnormalities in cerebral blood flow (CBF) and their relation to cognitive dysfunction. Global hemispheric tracer uptake relative to the cerebellum was similar in both groups, but regional over cerebellar activity was significantly reduced in the frontal cortex (85.9 +/- 5.1 vs 90.4 +/- 5.3; P = 0.01) and thalamus (99.2 +/- 8.8 vs 104.9 +/- 8.4; P = 0.05) of the HD patients. Normalization to whole-brain activity also showed the frontal cortex to be hypoactive in the HD patients, while tracer uptake was increased occipitally. These regional differences were not explained by the presence of atrophy or cerebrovascular damage seen on brain magnetic resonance imaging. The HD patients scored significantly worse on cognitive tests such as the Mini Mental State Examination (23 +/- 4 vs 28 +/- 1; P < 0.001) and Mattis Dementia Rating Scale (114 +/- 24 vs 143 +/- 1; P < 0.001). Regional activity ratios did not correlate with cognitive test scores, however. Our results indicate a disturbed pattern of CBF in HD patients, although regional SPET abnormalities did not correspond to the severity of cognitive dysfunction.