This paper discusses the general physical problems underlying the portrayal of ventricular geometry by ultrasonic techniques. This offers another means somewhat analogous to x-ray ventriculography for the detection of brain tumors. Progress is reported on studies of ultra-sound propagation properties in the tissues involved. Preliminary conclusions on safety thresholds of pain and damage are discussed. The most promising method to date is straight-through transcranial transmission (not echo ranging) utilizing changes in attenuation owing to differing amounts of ventricle along the transmission path. The optimum compromise frequency appears to be about 2.5 megacycles for which frequency results are reported on studies of receiver sensitivity and dynamic range, resolution, shielding, transducers, and presentation problems.