The response of large neutral amino acids (LNAA), glucose, and insulin plasma levels to a protein-rich and a carbohydrate-rich test meal was studied in anorectic patients (upon admission to hospital and after weight gain) and in a control group of young women. Patients showed reduced glucose tolerance, as well as increased and prolonged insulin secretion. After the protein meal, the ratio of tyrosine to other LNAA (a predictor of tyrosine flow into brain) was increased in patients and the ratio of tryptophan to other LNAA (a predictor of tryptophan flow into brain) depressed. The carbohydrate meal resulted in a smaller increase in the ratio of tryptophan to other LNAA in patients. Not all alterations showed a trend to normalization with weight gain. Implications of findings for monoamine metabolism and regulation of food choice are discussed.