1. 1. Smooth muscle contractility differed between non-hibernator (guinea pig) and hibernator (ground squirrel) species. In particular, in the hibernator the tonic receptor-mediated response was not Nifedipine-sensitive and was resistant to cooling 2. 2. Two Nifedipine-sensitive contractile components (phasic and tonic) were characteristic of smooth muscle from awake ground squirrels. This was altered during deep hibernation. Although smooth muscle from animals in deep hibernation was capable of producing a receptor operated tonic contraction, only a Nifedipine-sensitive phasic response was observed. This can be interpreted as a suppression of a voltage operated calcium channel during hibernation. 3. 3. The results support the hypothesis that the adaptive strategy for cold tolerance during hibernation may depend on subtle and selective regulation of cellular calcium influx.