The airway and cardiovascular effects of intravenous neurokinin A (NKA) and substance P (SP) were compared in six normal subjects. Both SP and NKA increased skin temperature (SkT) and heart rate (HR), but SP was more potent than NKA by factors of 6 and 20 respectively. No change in systolic blood pressure (BP) occurred with either peptide, but diastolic BP fell significantly with SP infusion. SP caused bronchodilation and NKA bronchoconstriction. NKA and SP have differing physiological roles and may activate different receptor populations.