The distribution of glucagon-like peptide-1-(7-36)amide like immunoreactivity (GLP-1-(7-36)NH2 IR) in rat brain was determined. Highest concentrations were found in the hypothalamus. A combination of gel chromatography and anion exchange chromatography showed that the majority of hypothalamic immunoreactivity exactly corresponded in position to synthetic GLP-1-(7-36)NH2. Chromatographic analyses of rat ileum demonstrated a similar pattern, whereas in rat pancreas mainly a large proglucagon fragment and GLP-1 were indicated. Determination of the subcellular distribution by differential centrifugation of hypothalamic tissue revealed that most of the GLP-1-(7-36)NH2 IR was present in the synaptosome fraction. GLP-1-(7-36)NH2 was released from hypothalamic tissue slices in a calcium-dependent fashion by potassium-induced depolarization. Thus GLP-1-(7-36)NH2 appears to fulfil two criteria for a neurotransmitter. No change was found in its hypothalamic content in streptozocin-induced diabetic rats compared to normal controls but a decrease was seen in hyperinsulinemic hyperglycemic KKAy mice compared to KK mice.