Plasma catecholamine concentrations in 40 patients shortly after accidental injury rose progressively with increasing severity of injury. Norepinephrine and epinephrine concentrations were unrelated other than by a common rise with severity; dopamine was closely related norepinephrine and not independently related to injury severity. Plasma glucose concentrations rose after injury; however, this was related only to the plasma epinephrine concentration and not independently to injury severity. Plasma lactate concentrations, in contrast, showed components related both to severity of injury and independently to norepinephrine and epinephrine concentrations. Plasma insulin concentrations were uniformly low, especially with respect to the hyperglycemia, in patients with high plasma epinephrine concentrations. Plasma concentrations of free fatty acids and of cortisol were unrelated to plasma catecholamine concentrations, as were pulse rate and blood pressure. These relationships confirm the expected role of the sympathoadrenal system in the metabolic changes following injury in man.