To evaluate the possible role of altered glucose metabolism in malignant cachexia, metabolic parameters including total glucose turnover, glucose oxidation, and Cori cycle activity were measured in fourteen patients with metastatic carcinoma. Eight patients with progressive weight loss (PWL) were compared to 6 without (controls). Cori cycle activity was significantly increased (p less than 0.02) in PWL patients, 90 mg/kg/hr (range, 22 to 193) compared to 18 mg/kg/hr (range, 13 to 24) in controls. Total glucose turnover was moderately increased in PWL patients, 196 mg/kg/hr compared to 110 mg/kg/hr in controls. Glucose oxidation was 62 mg/kg/hr versus 48 mg/kg/hr, and total caloric expenditure was 36 kcal/sq m/hr compared to 33 Kcal/sq m/hr. PWL patients were metabolically heterogenous and mean values are skewed by four patients with increased glucose turnover, oxidation, and markedly high recycling rates that were equivalent to total endogenous glucose turnover of a normal subject. Total caloric expenditure was greatest in three of the four patients with a marked increase in Cori cycle activity. Energy loss associated with a high rate of gluconeogenesis from lactate has been suggested as an explanation for increased energy expenditure in some cancer patients, thus contributing to mechanisms that promote weight loss.