Extracellular spikes were recorded simultaneously from dendrites and somata of Purkinje cells in thin cerebellar sections. Spontaneously occurring dendritic spikes were biphasic with the initial phase positive. Triphasic dendritic spikes with a large negative phase appeared during electrophoretic application of glutamate. In media containing procaine, tetrodotoxin, or high concentrations of KCl, negative dendritic spikes occurred whereas soma spikes were abolished. The negative dendritic spikes were suppressed by CoCl₂ or MnCl₂. Electrical stimulation elicited climbing fibre responses in somata and large negative waves in dendrites. Spikes of dendritic origin were different from those reflecting electrotonic spread of soma spikes. The relation between soma spikes and active dendritic spikes is discussed.