Synthetic, racemic lacinilene C methyl ether (LCME) causes slow-developing but strong and sustained contractions of canine tracheal smooth muscle when admin istered at ca. 1.92 x 10^-4 M, but causes only a weak response at a concentration of 0.64 x 10^-4 M. Based on the effect of verapamil and the absence of dramatic effects of methysergide, atropine, and pyrilamine, LCME appears to elicit contractions by enhancing the movement of calcium through membrane potential-dependent channels. This mechanism of action does not require activation of specific membrane receptors for serotonin, acetylcholine or histamine. A related, naturally occurring Gossypium sesquiterpenoid, 2-hydroxy-7-methoxycadalene (HMC), caused no significant response by the canine tracheal smooth muscle. Finally, an extraction procedure designed to obtain the basic, or alkaloid, substances in Coker 310 green bract provided 0.046% by dry weight of material which caused no significant response by the canine tracheal smooth muscle.