Head-injured patients were examined by a number of observers whose assessments were compared. Considerable discrepancies occurred when overall "levels" of consciousness and coma were used, and also with some terms which are in common use. More consistent assessments were obtained by employing the "Glasgow Coma Scale," which describes eye opening, verbal behaviour, and motor responsiveness. Nurses and general surgeons were as consistent as neurosurgeons when using this scale, and it was relatively resistant to language or cultural differences between observers. The practical reliability of the Glasgow scale enhances its value, both for monitoring individual cases and for making meaningful comparisons between series of patients with acute brain damage.