Plasma epinephrine (EPI) and norepinephrine (NE) were measured in conscious, unrestrained rats at rest, and following exercise, cold stress and hemorrhage. Heart rate and mean arterial pressure were monitored at all points. Minor modifications of a standard, commercially available methodology achieved good chromatographic separation of both EPI and NE. Sensitivity was sufficient for all NE measurements and for EPI measurements in the stress conditions. Estimates of EPI by this procedure were somewhat higher than those in other reports. Absolute values of NE, as well as the selective, qualitative changes found in both EPI and NE under each stress condition, were consistent with those found in other studies which used the radioenzymatic method. Blood withdrawal of two 1.5 ml samples, 3 hours apart, had no detectable effect on EPI, NE, mean arterial pressure or heart rate in otherwise non-stressed rats.