Dependency of histamine induced phasic and tonic contractions on intracellular and extracellular calcium in guinea pig tracheal smooth muscle was investigated. In Ca⁺⁺-free Krebs-Ringer solution, the phasic contraction caused by 10^-5 M histamine was not affected, but the tonic contraction declined much faster than that in normal Krebs-Ringer solution (KR). The phasic contraction in KR containing 3×10^-4 M dantrolene was depressed, but reached a level similar to that in normal KR, and the tonic contraction was maintained similarly with or without dantrolene. In KR containing organic calcium channel blockers, 10^-5M nilvadipine (FR34235), 10^-5 M verapamil or 10^-5 M diltiazem, neither phasic contraction nor tonic contraction was affected. No contraction was observed in Ca⁺⁺-free KR containing 3×10^-4 M dantrolene. These results suggested that the phasic con traction by histamine depended on the intracellular calcium and the tonic one, on the extracellular calcium, and the organic calcium channel blockers had no effect on both phasic and tonic contractions caused by histamine.