In vitro, median eminence was found to take up <sup>3</sup>H-LRF rapidly, reach equilibrium in approximately 30 min, and achieve an uptake (30 pg LRF/mg) twice that accumulated by anterior pituitary. Conditions which challenged cellular integrity (boiling, treatment with hypertonic saline, etc.) caused marked increases in uptake. Uptake was temperature-dependent and required oxygen and glucose, but was not noticeably ouabain-sensitive. The dissociation of <sup>3</sup>H-LRF from median eminence occurred rapidly into media containing a 1,000-fold greater concentration of unlabeled LRF. Estradiol and testosterone, but not corticosterone, significantly inhibited uptake. Unlabeled LRF and TRF, but not MIF, provided significant competition for the uptake of <sup>3</sup>H-LRF.