This study investigates the binding of [3H]harmane to rat whole brain homogenates. Saturation studies revealed [3H]harmane labels a single, saturable, high-capacity population with high affinity. All the test compounds displaced [3H]harmane completely and in an apparently monophasic manner. The displacement profile of the test ligands indicated labeling of MAO-A. Given the high level of MAO-A binding, it is unlikely that a low-capacity I2 site would be distinguishable from the total [3H]harmane population.