A superconducting sensor was used to measure the magnetic field evoked from the isolated cerebellum of the turtle by brief electrical stimulations of the dorsal surface. The field was generated by neuronal activities, since its amplitude was reduced when Mn²⁺ was applied and completely abolished with tetrodotoxin. In normal bathing medium, the field amplitude at a distance of 17 mm was as much as 1 pT, demonstrating that the magnetic technique can be used to remotely monitor neural activities in regions of 10 mm³ or even less.