A computer-based approach for instruction and diagnosis of clinical acidbase disorders has been developed. Its significant features are the following: (1) consideration of a differential diagnosis list (rather than a single diagnosis) for any given blood pH plus either carbon dioxide content, bicarbonate level, or partial pressure of carbon dioxide; (2) use of ancillary clinical and laboratory information about the patient to arrive at the most likely diagnosis from the differential diagnosis list; (3) adaptability to users of widely differing clinical expertise and educational backgrounds; and (4) provision for tabulating the relative frequencies of acid-base disorders presented to the computer. The computer's differential diagnosis is based on an acid-base map. A sample case illustrates the logical process involved. This program demonstrates that the computer can mimic the clinical consultant in its approach to diagnosis and in its ability to teach.