In previous research using young male subjects, the Type A behavior pattern was linked with cardiovascular and neurohormonal hyperresponsivity to laboratory stressors. The main objective of the present study was to determine whether the positive association between the Type A pattern and such physiological hyperreactivity is also present among healthy middle-aged men. Subjects were 28 middle-aged (35-50 years) white males who were classified as Type A (n = 16) or Type B (n = 12) on both the Structured Interview and the Jenkins Activity Survey. In two laboratory sessions, one week apart, subjects participated in either a mental arithmetic task or a sensory intake task. Twenty-four-hour urine collection was completed on a third day. Results showed that while no A/B differences in reactivity to either task were found, Type A subjects exhibited chronic elevation of plasma neurohormones on both laboratory days. The catecholamine elevations found across experimental periods on two laboratory days among Type A men generalized to more naturalistic settings, as indexed by 24-hr urinary excretion rates. The chronic elevations in both sympathetic nervous system and hypothalamic-pituitary-adrenal axis function we observed in middle-aged Type A men could account for epidemiological findings of increased coronary risk in this group.