In isolated rat diaphragm strips, halothane augments the tension produced daring caffeine-induced contractures in a dose-related manner. Potassium-induced contracture tension is augmented in the presence of halothane to a concentration of 0.75 per cent, and decreased at halothane concentrations of more than 1 per cent. The time to peak tension for potassium-induced contractures is diminished by all halothane concentrations. T-tubular disruption by hypertonic glycerol does not alter anesthetic-induced augmentation of caffeine-induced contractures. It is postulated that halothane augments calcium-release processes in sarcoplasmic reticulum. Membrane events or excitation-contraction coupling steps may be also altered by halothane.