Adetailed stereotaxic atlas is presented of the mesencephalon in the albino rat of the Charles River derived (CD) strain. The Kopf stereotaxic frame was used and the head positioned to allow easy surgical access to the mesencephalon. To insure proper positioning of the head before operative intervention, the alignment was checked by two sets of measurements: the distance between earbars, and measurements of the coordinates of bregma and lambda. Because some structures are not easily approached stereotaxically without traversing other parts of the midbrain and supratentorial regions, an oblique approach was tested and found useful. Of 18 test lesions, 14 were within 0.25 mm of the target.