Electrolytes are essential to normal skeletal muscle contraction and are thought to play a role in muscle fatigue. Excess accumulation of ammonia and hydrogen ions after strenuous bouts of physical activity are thought to slow muscle contractions and decrease muscle tension development. Certain disease states cause abnormal levels of such electrolytes as calcium, magnesium, potassium, or sodium. Excessively high or low levels of these ions in the serum are associated with symptoms such as muscle weakness or cramping. Nurses should know the effects of abnormal electrolyte levels on muscle function in the assessment and treatment of their patients.