In this article, the second in a new series designed to improve acute care nurses' understanding of laboratory abnormalities, the author continues her discussion of important values in the basic metabolic panel (see Back to Basics, January, for a discussion of sodium and fluid balance). Here she addresses the electrolytes potassium and chloride as well as blood urea nitrogen and creatinine, four values that are best considered together because they both reflect and impact renal function as well as acid-base homeostasis. Important etiology, clinical manifestations, and treatment concerns are also presented. Three case studies are used to integrate select laboratory diagnostic tests with history and physical examination findings, allowing nurses to develop a thorough, focused plan of care for electrolyte abnormalities and kidney disorders commonly encountered in the medical-surgical setting.