This study was initiated to determine if factors exist in the blood or cerebrospinal fluid (CSF) of the domestic fowl that act upon the central nervous system to control food intake. Plasma collected from free-feeding and 24-hour fasted leghorn cockerels was lyophilized, reconstituted to 2, 4, or 5 times the original concentration, and injected, via a stereotaxically implanted 23 gauge stainless steel guide cannula, into the lateral ventricle of free-feeding leghorn cockerels. Food intake was significantly reduced following injection of 2, 4, and 5 times normal concentration of plasma from free-feeding birds. Plasma from fasted birds did not alter food intake regardless of concentration, but did significantly reduce water intake when concentrated to five times normal. A similar study was conducted with fractions of plasma of different molecular weight ranges. Plasma collected from free-feeding cockerels was partitioned by gel filtration into the following molecular weight fractions: >5000 molecular weight, <5000 molecular weight, 1500-5000 molecular weight, and <1500 molecular weight. The fractions were lyophilized and reconstituted to four times the original concentration and injected into the lateral ventricle of free-feeding leghorn cockerels. Food intake was significantly decreased by the <5000 and <1500 molecular weight fractions, whereas water intake was not affected. The 1500-5000 molecular weight fraction and the fraction above 5000 did not affect food or water intake. To determine if this food intake inhibiting factor existed in the cerebrospinal fluid (CSF) of the domestic fowl, CSF was collected from free-feeding and 24-hour fasted broilers and injected into the lateral ventricle of leghorn and broiler cockerels. Food intake was not affected by either the normal or four-times normal concentration of CSF collected from free-feeding or 24-hour fasted broilers. Water intake was significantly increased in the leghorn and broiler birds receiving the four times normal concentration of CSF collected from 24-hour fasted birds, but was not affected in the birds receiving CSF collected from the free-feeding donors. It appears, therefore, that a food intake inhibiting factor exists in the plasma of the free-feeding domestic fowl that does not exist in the CSF. / Ph. D.