Slow variations of the magnetic field were recorded in real time during spreading depression (SD) in the isolated turtle cerebellum. The magnetic signal lasted for 2-10 min with the largest amplitude in the first minute. The field strength was of sufficient magnitude to be measured unaveraged at 2-4 cm from the tissue. The directions and time course of the magnetic signal indicated that cerebellar SD is accompanied by current normal to the cerebellar surface. The observations reported here are of clinical interest due to the potential involvement of SD in various neurological disorders, notably head trauma and migraine.