The relation between left ventricular wall thickness and mass, arterial plasma catecholamines, and blood pressure at rest and during a mental arithmetic challenge and a cold pressor test was examined in 69 healthy men 19 years of age. The subjects were recruited from the 1st (n=21), 50th (n=26), and 99th (n=22) percentiles in mean blood pressure. All underwent echocardiography to determine mean wall thickness and left ventricular mass. Continuous intra-arterial blood pressure, electrocardiogram, and arterial sampling of plasma catecholamines were performed after 30 minutes of supine rest, during a 5-minute mental arithmetic challenge, and during a 1-minute cold pressor test. Stepwise multipleregression analyses considering mean wall thickness and left ventricular mass as the dependent variables were applied. Intra-arterial systolic blood pressure (r=.54, P<.0001) and arterial plasma epinephrine (r=.31, P=.009) after 30 minutes of supine rest were the only independent explanatory variables of mean wall thickness (multiple R2=.33, P<.0001). Blood pressure at screening and during mental stress and cold pressor tests were not independent explanatory variables. The present study suggests that resting arterial blood pressure and plasma epinephrine may be of importance for development of left ventricular hypertrophy.