1 Concentration-effect curves to acetylcholine and histamine were produced in fresh human bronchial muscle (2 to 4 h after removal from the patients) and in preparations previously stored at 4 degrees C for 12 h. 2 Sensitivities of fresh human airway muscle preparations to acetylcholine (pD2 value, 5.89 +/- 0.03; n = 4) and histamine (pD2 values, 5.41 +/- 0.03; n = 13) were similar. There was no significant difference in the sensitivities of stored preparations (acetylcholine: pD2 value, 5.70 +/- 0.06; n = 23 and histamine: pD2 value, 5.44 +/- 0.07; n = 16) when compared to the fresh preparations. 3 Indomethacin did not significantly change the basal tone in preparations of either fresh or stored human airway muscle. 4 A low concentration of indomethacin (0.17 muM) significantly reduced responsiveness and sensitivity to histamine in stored bronchi but not in fresh bronchi. The acetylcholine concentration-effect curves were unaltered by exposure to this concentration of indomethacin in either fresh or stored tissues. High concentrations (1.7 muM and 17 muM) depressed the maximal responsiveness of the bronchi to both agonists. 5 These results suggest indirectly that the regulatory role of prostaglandins in human airway muscle may be different from that in other species.