Cancer cachexia is a poorly understood phenomenon that contributes to patient intolerance of operations, radiation, and chemotherapy. Reversal of this dysmetabolic state has been attempted by administration of carbohydrates, proteins, and lipids, with little demonstrated clinical benefit. Identification of elevated serum triglycerides (TG) in two tumor-bearing (TB) animal models and recently reported in humans with cancer may be a part of this dysfunctional state. Because lipids makeup energy repletion in patients receiving TPN, the question of how exogenous lipids affect these TB animals needed to be resolved. Intralipid administered by intravenous or gastrointestinal routes raised serum levels in TB animals to greater than 600 mg/dl, even when their baseline TG levels were comparable to nontumor-bearing control animals. The addition of glucose concomitantly with Intralipid failed to prevent TG levels from rising abruptly. Increased lipolytic activity in TB sera was demonstrated and that was not due solely to hypoglycemia or hypoinsulinemia. Administration of lipids to TB animals results in excessively high serum TG levels that appear to be due, in part, to the demonstrated lipolytic activity in TB animal sera.