Amino acid levels were measured in perfusates from biplanar slices of rat cerebellum installed in a Krebs-filled three-compartment chamber. The two lateral compartments housed the white matter and a section containing parallel fibres respectively. The central compartment housed cortical structures, including the Purkinje cell and granule cell bodies. This arrangement allows selective electrical stimulation of the parallel fibre or mossy fibre pathways, recording of the evoked responses to such stimulation and collection of the perfusion medium passing through the central chamber for amino acid analysis using high-pressure liquid chromatography (HPLC). Both, 2-Hz and 5-Hz stimulation of white matter caused a delayed increase in arginine levels in the perfusate. Since L-arginine is the physiological precursor of nitric oxide, a neuronal messenger in the brain, the data suggest that physiological stimuli can result in the release of this precursor, possibly to supply the nitric oxide synthase.