The distribution of the messenger RNA coding for the recently cloned cannabinoid receptor was studied for the first time in the human brain using in situ hybridization histochemistry and oligonucleotides probes. Microscopically, positive neurons were observed in the layers II-III and V-VI of the cerebral cortex, and in the hilus and the different dendritic layers of the dentate gyrus and Ammon's horn of the hippocampus. No additional microscopic signal could be detected. Macroscopically, a slight hybridization signal, visible on the films after 2 months exposure and which disappears after RNAse treatment, was also found throughout all layers of the cortex, in the pyramidal cell layer of the hippocampus, in the caudate and putamen, and in the granular and molecular layers of the cerebellum. No signal was detected in the brainstem, spinal cord and white matter. In conclusion, the cannabinoid receptor mRNA neuronal localizations here demonstrated in the human brain confirm our previous report in the rat, taking into account that the levels of the transcripts found in the human were lower than in the rat brain.