1 h after intravenous administration, 3H-DH-ergot alkaloids showed maximal uptake in the range of 10-5M in various visceral organs, and of 10-7M in most parts of the CNS of the cat. The clearance function in both groups of tissues was logarithmical linear, the slope of the straight line for the parts of the CNS being considerably flatter. Repeated administration of these drugs demonstrated a higher retention in the CNS than in the other organs. The single-dose level in the CNS is reinforced and, in contrast to liver and lung, maintained for at least 24 h.