Plasma concentrations of free and sulfoconjugated catecholamines were measured in healthy infants and children under resting conditions. Free norepinephrine and epinephrine levels were up to three times higher in healthy children under 2 years than in adults, even under true resting conditions. In contrast, free dopamine concentrations of all age groups fell within the normal range for adults. The levels of sulfoconjugation were in the adult range.