Locustamyoinhibiting peptide (Lom-MIP) is one of the 4 identified myoinhibiting neuropeptides, isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion complexes of the locust, Locusta migratoria. An antiserum was raised against Lom-MIP for use in immunohistochemistry. Locustamyoinhibiting peptide-like immunoreactivity (Lom-MIP-LI) was visualized in the nervous system and peripheral organs of Locusta migratoria by means of the peroxidase-antiperoxidase method. A total of 12 specific immunoreactive neurons was found in the brain. Processes of these neurons innervate the protocerebral bridge the central body complex and distinct neuropil areas in the proto- and tritocerebrum but not in the deuterocerebrum nor in the optic lobes. The glandular cells of the corpora cardiaca, known to produce adipokinetic hormones, are contacted by Lom-MIP-LI fibers. The corpora allata were innervated by the nervus corporis allati I containing immunoreactive fibers. Lom-MIP-LI cell bodies were also found in the subesophageal ganglion, the metathoracic ganglion and the abdominal ganglia I-IV. In peripheral muscles, Lom-MIP-LI fibers innervate the heart, the oviduct, and the hindgut. In the salivary glands, Lom-MIP-LI was detected in the intracellular ductule of the parietal cells. Possible functions of Lom-MIP are discussed.