WE report the distinct cellular distribution in the human cerebellar cortex of the mammalian mt1(Mel1a) and MT2(Mel1b) (1) melatonin receptor subtypes. Specific binding of the non-selective radioligand 2-[125I]iodomelatonin to the outer molecular layer was significantly higher than to the granule cell layer. Melatonin receptor subtype expression was assessed byin situhybridization using selective and specific digoxigenin-labeled antisense oligonucleotide probes. This is the first demonstration of MT2melatonin receptor mRNA expression in human cerebellar Bergmann glia and astrocytes. On the other hand, the mt1melatonin receptor mRNA was expressed in both basket-stellate cells and granule cells. We conclude that mt1and MT2melatonin receptors are heterogeneously expressed in human cerebellar cortex.