We examined the relative genetic and environmental influences on the variability in plasma epinephrine, norepinephrine, and dopamine levels in 109 twin pairs. Epinephrine levels were lower in females (P = 0.048). The norepinephrine concentration increased with age (r = 0.40; P < 0.001). Blood pressure (BP) was not associated with epinephrine levels in either sex or with norepinephrine levels in females. In males, there was a positive association between norepinephrine concentration and diastolic BP (r = 0.31; P = 0.020). A negative association between dopamine levels and systolic and diastolic BP in females (r = -0.22; P = 0.014 and r = -0.20; P = 0.027, respectively) was not maintained after accounting for age, body mass index, and sex. Using path analysis and maximum likelihood model fitting, genetic, unique environment, and age effects contributed 57% (P < or = 0.001), 27% (P < or = 0.001), and 16% (P < or = 0.001) to the variability in norepinephrine, respectively. Genetic effects explained 64% (P < 0.1) and 74% (P < 0.1) of the variability in epinephrine concentrations in females and males, respectively. Unique environmental influences explained the remainder. Genetic and unique environmental effects explained 72% (P < 0.01) and 28% (P < or = 0.001) of the variability in dopamine levels. These results indicate a substantial genetic influence on plasma catecholamine levels. Although consistent associations between plasma catecholamines and BP were not evident in this study, the observed genetic influence on circulating catecholamines may be relevant to the potential role of the sympathetic nervous system in the early stages of essential hypertension.