Frog muscles bathed in solutions equilibrated with 0.5%-2.0% halothane develop large contractures when cooled to 2-4 degrees C. These halothane-cooling contractures (HCC) are dose dependent and reproducible; they are potentiated by lidocaine (5 mM), abolished by procaine (5 mM), and partially inhibited by procainamide (5 mM) or sodium salicylate (2 mM). The HCC provides a simple model system for investigating the effects of low halothane concentrations on Ca homeostasis and contractility in skeletal muscle.