Digitalis intoxication is among the most common serious adverse drug reactions in clinical medicine. While the recent development of a radioimmunoassay to accurately measure serum concentrations of digoxin has been of assistance, digitalis intoxication remains a difficult diagnosis to make with certainty. The difficulty in diagnosing digitalis intoxication arises from the nonspecificity of its associated signs and symptoms. The most common symptoms include fatigue, weakness, nausea, and anorexia. These symptoms can occur with many illnesses other than digitalis intoxication. Similarly, the electrocardiographic disturbances caused by cardiac glycosides may be nondiagnostic. The arrhythmias commonly associated with digitalis toxicity are often nonspecific and can be a reflection of the patient's underlying heart disease. The measurement of serum digoxin levels is useful, but studies have demonstrated overlap of the levels between groups with and without toxicity. Due to the modulation of the cardiac effects of digitalis glycosides by such clinical variables as underlying myocardial or renal disease, electrolyte and acid-base imbalances, and other factors, the correlation of toxicity with particular serum digoxin concentrations may vary. Because of the inherent difficulties in confirming the diagnosis of digitalis intoxication in some cases, digoxin-specific Fab antibodies may play a role as a diagnostic tool. Certainly, digoxin-specific Fab antibodies play a significant part in the treatment of digitalis intoxication. Fab antibodies have been successfully used to reverse the effects of digoxin, digitoxin, and oleander poisoning. These antibodies are useful in the treatment of acute and chronic digitalis intoxication in all age groups, including geriatric and pediatric populations.(ABSTRACT TRUNCATED AT 250 WORDS)