ATP-sensitive channels were observed in isolated inside-out membrane patches from rat cultured central neurones. Two types of ATP-sensitive K⁺ channels were present in cortical neurones, one which had its open-state probability increased, the other its open-state probability decreased by application of ATP to the cytoplasmic membrane surface. Another, ATP-sensitive channel differing in ion conductance from all previously reported ATP-sensitive channels was also seen in patches from cortical neurones. This channel was noselective with respect to Na⁺, K⁺ and Cl⁻ ions and ATP produced a “flickery” type of block. The non-hydrolysable analogue, AMPPNP, did not mimic ATP and prevented ATP action Preliminary experiments indicate that similar, but not, identical ATP-sensitive channels exist in cerebellar neurones