In six dogs, the authors investigated the effect of balothane on cardiac acceleration response to the electrical stimulation of a cutaneous nerve. It was found that increasing the concentration of halothane was associated with a proportional depression of the cardiac acceleration response to somatic nerve stimulation (y—99.8 - 44.3x; y—δHR, x—halothane end-tidal concentration). Relationship of the response to end-tidal anesthetic concentration was characterized by a strong correlation (r = −0.93,P< 0.0001). Complete abolition of the increase in heart rate in response to somatic nerve stimulation was observed at a halothane end-tidal concentration of 2.2 vol% (extrapolation). It is suggested that suppression of heart rate increase to noxious stimulation may be used as a graded index of the depth of anesthesia for halothane.