The effects of incubation conditions on the frequency of spontaneous action potentials exhibited by guinea-pig cerebellar slices, and recorded with an extracellular microelectrode, have been investigated. Various incubation conditions that lead to tetrodotoxin-sensitive uptakes of water and of sodium ions by the incubated cerebellar slices lead to enhanced frequencies of the spontaneous action potentials, e.g. the presence of protoveratrine or of ouabain, the absence of glucose or the onset of anoxia. The frequency of the spikes is also enhanced by acetylcholine (in presence of neostigmine) or by the presence of excitatory amino acids, such as L-glutamate, D-glutamate or L-aspartate. It is suppressed by tetrodotoxin, or by the inhibitory amino acids, e.g. $\gamma $-aminobutyrate, glycine or taurine, or by ammonium ions or by pentobarbital. It is concluded that guinea-pig cerebellar slices, incubated under specified conditions, may provide a suitable means for quantitative correlation of neurochemical data with data obtained by electrophysiological techniques in tissue incubated under similar conditions and also for quantitative assessment of the effects of amino acids on cerebellar electrical activity.