Structural brain abnormalities have recently been discovered using magnetic resonance imaging in infantile autism, a neurodevelopmental disorder of unknown etiology. However, functional neuroimaging studies in autism using positron emission tomography have had conflicting results and have not explained how the known structural brain abnormalities in autism act in a functioning brain to produce autistic behavior. Using a new technology, high-resolution brain single photon emission tomography, we studied and scanned four young adults with infantile autism and four age-matched controls using the labeled ligand 99mTc-D,L-hexamethyl-propylene amine oxime (99mTc-HMPAO). Total brain perfusion was significantly decreased in autism subjects (range, 58% to 72% of controls, p less than or equal to .02). In addition to the globally decreased perfusion, the autism group also had regionally decreased flow in the right lateral temporal and right, left, and midfrontal lobes compared with controls (p less than or equal to .02, Mann-Whitney t-test).