MANY neurons in the cat primary visual cortex are sensitive to cruciform and corner figures consisting of two oriented lines. To determine the contribution of inhibition to this property we investigated 85 V1 neurons before and after local blockade of GABAergic inhibition by microiontophoretic application of bicuculline. Cross sensitivity was generated or enhanced by inhibition in roughly 1/3 and suppressed or diminished in another 1/3 of the cells. In the remaining 1/3 cross sensitivity was either absent or not influenced by inhibition. The results demonstrate a substantial contribution of intracortical inhibition to either establish sharp single bar orientation tuning or to generate or modulate the sensitivity of visual cortical neurons to line crossings.