An elderly woman living independently with some help from her family is brought to the local emergency room because she is confused and vomiting. While her son suspects a stroke, a quick battery of laboratory tests indicates that her current problems are the result of impaired kidney function, an old-fashioned home remedy for ulcers, and her prescribed blood pressure medication. The combination of patient- and drug-related factors produces an acid-base disorder responsible for her confusion. This disorder further disrupts her kidney function. The case illustrates secretion and reabsorption processes in the kidney tubule which regulate plasma and urinary electrolytes (including calcium) and pH. The role of bicarbonate in maintaining systemic pH is emphasized. Interactions among the renal, respiratory and nervous systems in the regulation of systemic pH are also illustrated. Further, basic principles of pharmacotherapy and issues related to the appropriate use of medications are introduced. The case was developed for use in a physiology or human anatomy and physiology course, but it might be used in undergraduate nursing courses as well (e.g., pharmacology, pathophysiology).