In acute experiments on 38 lightly anesthetized cats, the septal region of the forebrain and the hypothalamus were explored for loci whose activation by electrical stimulation produced, suppressed or failed to affect shivering. Shivering was consistently and repeatedly produced by stimulation of the dorso-medial region of the posterior hypothalamus, and sometimes by stimulation of the ventrolateral region of the septum. A greater intensity of stimulus was needed to produce more latent and less intense shivering during septal than during hypothalamic stimulation. Similarly, more intense stimulation was necessary to suppress shivering during ventromedial septal stimulation than during anterior, or ventrolateral posterior hypothalamic stimulation. The most effective stimulation frequency for both activation and suppression of shivering was 50 pulses/sec, i.e. fivefold the evoked or suppressed limb tremor frequency. On the basis of these results it was concluded that septa! influences on shivering are secondary to a primary hypothalamic modulation of this tremor. Such modulation appears to be more concerned with initiation and maintenance than with the rhythm of shivering.