鈥� Blood pressure, peripheral blood flow, and peripheral vascular resistance were measured in normal adults and children and in children with autism and severe disturbances in personality development while the individuals were engaged in a variety of attentional tasks. The tasks were designed to elicit outward direction of attention (and intake of sensory input) or inward direction of attention (and relative rejection of external sensory input). During tasks involving sensory rejection, normal adults and normal children showed increased blood flow and decreased peripheral vascular resistance; with sensory intake, blood flow was decreased and resistance was increased. The most severely impaired children showed little alteration in their physiological response to task requirements. Autistic children had higher mean blood flow and lower peripheral vascular resistance than normal children and adults. Some autistic children characteristically may be in a state of sensory rejection associated with generally higher levels of arousal or defense against environmental bombardment.