Concentrations of plasma norepinephrine (NE) and plasma-3-methoxy-4-hydroxyphenylglycol (MHPG), blood pressure, and heart rate were measured on 2 days in 25 depressed patients and 25 controls. Comparisons were made between patients and controls, and also between days for both groups, to determine the short-term stability of these measures. The means of the plasma and urinary noradrenergic metabolite measures were not significantly different between groups. The variance of plasma MHPG, plasma NE, and mean blood pressure was greater in the depressed patients than in controls. Blood pressure, plasma MHPG, and plasma NE were relatively stable as suggested by the significant correlations between the 2 days for each of these variables. Plasma NE, plasma MHPG, and the sum of the deaminated urinary metabolites (MHPG and vanillylmandelic acid) were significantly intercorrelated. These results support other data in suggesting that plasma concentrations of NE and MHPG may be useful measures of noradrenergic activity, but may not consistently distinguish depressed patients from controls.