Hypothalamic concentrations of six regulatory peptides having central effects on appetite and/or glucoregulation were measured by radioimmunoassay in spontaneously-diabetic Chinese hamsters and in age- and sex-matched non-diabetic control animals. In the diabetic hamsters, hypothalamic concentrations of somatostatin and neuropeptide Y were significantly reduced by 25-30% below controls. None of the other four peptides examined (bombesin, galanin, neurotensin and vasoactive intestinal peptide) differed significantly between the two groups. Disturbances in neuropeptide Y (the most potent central appetite stimulant yet discovered) and in somatostatin could be related to hyperphagia, an early and possibly primary abnormality of the diabetic syndrome in the Chinese hamster.