Visual receptive fields of 42 LGN cells from normal cats and 110 cells from striped cylinder-reared kittens were studied with the aid of a computer controlled optical system. In the normal cats, ten of the 42 cells were weakly biased for orientation of the visual stimulus when tested with bars swept through the receptive field. Of those ten, eight were classified as transient. The orientation preferences of the ten biased units appeared randomly distributed around the clock. Of the LGN cells from the cylinder-reared group, about half of the transient cells had weak biases for orientation; only 7% of the sustained cells had biases. The orientation preferences of the biased LGN cells in the stripe-reared animals were either parallel to or orthogonal to the stripes each animal saw during its time in the conditioning cylinder. In 16 out of 18 of the biased LGN cells it was found that increasing the velocity of the test target reduced or eliminated the bias apparent at the lower velocity. For some LGN cells special techniques, such as inhibition of activated discharge, were needed to reveal orientation biases. The results described here, considered with data from others, suggest a role for the corticofugal projection in modulating the responses of some LGN cells.