In this article, the author describes a method developed by Dr. William T. Lipscomb for teaching blood gas analysis of acid-base status and provides three examples using Willie's acid-base box. Willie's acid-base box is constructed using three of the parameters of standard arterial blood gas analysis: (1) pH; (2) bicarbonate; and (3) CO[subscript 2]. Therefore, it depicts the Henderson-Hasselbalch equation in a simple visual form that requires no calculations. The top value depicts the pH with the normal range of 7.35-7.45 and is considered inside the box. Anything below that range is outside the box and identifies acidosis, whereas any value above the range is outside the box to the right and depicts alkalosis. The middle line represents the metabolic component of the acid-base system, which is measured clinically as bicarbonate. This method works well with almost all but the most complex acid-base problems and should be of benefit to both medical and nursing students. (Contains 3 figures.)