The technique of A-scan echoencephalography is criticized in so far as it lacks objectivity and reproducibility. In the author's laboratory, the M-echo, being of higher amplitude than other intracranial echoes, is distinguished from other echoes by an averaging technique-a time exposure. Double transmission pulses indicate the theoretical position of echoes from the true mid-line and superimposition of far-side echoes ensures that the transducers are correctly aligned.The very considerable difficulties in identifying the anatomical structures giving rise to other echoes seen within the skull are outlined. They are largely due to variations in the reflected energy, depending upon the shape and orientation and position of the various interfaces with respect to the ultrasonic beam.Despite these difficulties and limitations, A-scan echoencephalography appears to have an important part to play as a simple, safe and quick form of neurological examination, if the technique can be made truly objective.