A new expression for the streaming potential of a charged channel is derived. It reduces to the classical result in the large pore limit. It is particularly well suited to application to biological channels-channels that contain only a small number of ions whose motion may be correlated and which are not axially uniform. The derivation is based on a calculation of the volume of water carried by each ion that traverses the channel and makes use of the reciprocal theorem of Lorentz. An estimate of the contribution to the streaming potential of the wide region of biological ion channels is presented. The derivation uses a set of assumptions and conditions that differ significantly from previous derivations and may be useful for nonbiological applications.