The critical current densities across grain boundaries have been measured as a function of misorientation angle in the basal plane of bicrystals of Y Ba 2 Cu 3 O 7− δ. For small misorientation angles, the ratio of the grain-boundary critical current density to the bulk critical current density is roughly proportional to the inverse of the misorientation angle; for large angles, this ratio saturates to a value of about 1 50. These results imply that achieving a high degree of texture both normal to and within the basal plane is important for the obtaining of very high critical currents in pure polycrystalline samples.