Transient receptor potential (TRP) ion channels comprise a newly identified family of cation-permeable channels (Nilius & Voets, 2005). Here we detail evidence that choroid plexus exhibits a non-selective cation channel with similarities to TRP channels. Fourth ventricle choroid plexus were isolated post mortem from mice. Cellular currents were determined by whole cell patch clamp on intact tissue fragments. The standard bath solution was a high NaCl Ringer solution. The pipette solution was low Cl^– with aspartate being the principal anion and Na⁺ the principal cation plus 5mM ATP and 5mM BAPTA. K⁺ was omitted from all solutions. Reversal potentials were determined by polynomial regression of current-voltage records and inward conductance was measured between Vm = -120 to -100 mV. Data are expressed as means ± SEM and statistical significance was tested using Student’s t test and assumed at the 5% level. Mouse choroid plexus epithelial cells exhibited an inwardly rectifying conductance of 128 ± 24 pS/pF (n=20). The reversal potential was -2.6±1.3mV, suggesting a non-selective conductance. To investigate the identity of the inwardly rectifying conductance in more detail the effect of substituting bath Na⁺ for other monovalent cations was examined. Replacing bath Na⁺ with Cs⁺ increased inwardly rectifying conductance to 596±74 pS/pF (n=5) whereas Li⁺ and NMDG⁺ caused the conductance to decrease to 30±6 and 17±3 pS/pF, respectively (n=9/5). The corresponding cation selectivity sequence of the inwardly rectifying conductance was equally selective for Cs⁺ and Na⁺ and much less selective for Li⁺ and NMDG⁺. Addition of 100µM gadolinium inhibited the conductance by 81±2% with no effect on outward current. These data show that the epithelial cells of the choroid plexus express a non-selective cation conductance which is inhibited by gadolinium. The properties of the conductance described here are similar to those of some TRP channels, notably TRPM3, mRNA for which has recently been identified in murine choroid plexus tissue (Oberwikler et al. 2005).