Long-term records of the free-running food intake rhythms were obtained from 26 young adult blinded rabbits that were subjected in the course of recording to bilateral superior cervical ganglionectomy (sympathectomy). This always resulted in acceleration of the rhythm (mean delta tau = -0.35 h). Some 4 months afterwards, 12 rabbits were pinealectomized and after another 4 months sham pinealectomized also. In the other 14 animals, these operations were performed in the reverse order. It appeared that suctioning away part of the ventricular walls during sham pinealectomy was followed by a slight reduction in tau (mean = -0.07 h) that could be largely attributed to the spontaneous gradual reduction of tau that occurred throughout all experiments. On the other hand, total pinealectomy in these already sympathectomized blinded rabbits always resulted in a substantial deceleration of the rhythms (mean delta tau = +0.23 h). These observations on blinded rabbits suggest that a sympathetically denervated pineal gland releases appreciable amounts of melatonin or of another hormone with a melatonin-like accelerating effect on the circadian pacemaker (SCN).