Spreading depression (SD) was elicited in the benzoate-conditioned rat cerebellum by microinjection of KC1. Median SD propagation velocity was 9.2 mm . min-1. [Na+]0 decreases, median value 77.5 mM, were measured with ion-selective micropipettes. Superfusion of the cerebellum with 10-5 M tetrodotoxin did not modify the propagation velocity or decrease the [Na+]0 change. This confirms that classical voltage-mediated Na+ conductances are not involved in SD.