<jats:title>Abstract</jats:title><jats:p>The pharmacological effects of crychine, isolated from Cryptocarya chinensis Hemsl, on rat thoracic aorta were examined. In the high-K+ medium (60 Mm), Ca2+ (0·03–3 Mm)-induced vasoconstriction was inhibited by crychine in a concentration-dependent manner (10–100 μg mL−1). Increasing the incubation time from 5 to 30 min did not cause more pronounced inhibitory effect on KCl-induced contraction. The tonic contractions elicited by KCl (60 Mm) and Bay K 8644 (0·1 μm) were also relaxed by the addition of crychine and were more marked in the 1·9 Mm than in the 5 Mm Ca2+ medium. The noradrenaline concentration-response curves were antagonized non-competitively by crychine (10–100 μg mL−1). At the plateau of noradrenaline-induced tonic contraction, the addition of crychine also caused relaxation. This relaxing effect of crychine was not antagonized by indomethacin (20 μm) or methylene blue (50 μm), and was still present in denuded aorta or in the presence of nifedipine (2 μm). Caffeine (10 Mm)-induced contraction and cAMP or cGMP levels were not affected by crychine. It is concluded that crychine relaxes the rat thoracic aorta mainly by suppressing the Ca2+ influx through both voltage- and receptor-operated calcium channels.