We have developed and employed a stereotaxic coordinate system for the pig brain based on eternal skull landmarks. Sagittal, coronal, and horizontal planes were defined. Based on histological maps and ventricular casts, the coordinates for locating the lateral ventricles were described. Guide tubes leading to the lateral ventricles have been chronically implanted. This access route to the ventricular system has been used for stimulation of the dipsogenic response with angiotensin and for withdrawal of cerebrospinal fluid. Solved and unsolved problems arising with these procedures have been defined.