Anorexia and weight loss are negative prognostic factors in patients with cancer. Although total ghrelin levels are increased in energy-negative states, levels of the biologically active octanoylated ghrelin and the anorexigenic peptide YY (PYY) have not been reported in patients with cancer-induced cachexia. We hypothesized that abnormal ghrelin and/or PYY levels contribute to cancer-induced cachexia. We evaluated 21 patients with cancer-induced cachexia; 24 cancer patients without cachexia; and 23 age-, sex-, race-, and BMI-matched subjects without cancer. Active ghrelin levels and the active to total ghrelin ratio were significantly increased in subjects with cancer-induced cachexia, compared with cancer and noncancer controls. PYY levels were similar among groups. Appetite measured by a visual analog scale was not increased in subjects with cachexie. The increase in active ghrelin levels is likely to be a compensatory response to weight loss. Cachexia may be a state of ghrelin resistance because appetite does not correlate with ghrelin levels. Changes in the active to total ghrelin ratio suggest that a mechanism other than increased secretion must be responsible for the increase in active ghrelin levels. PYY is unlikely to play an important role in cancer-induced cachexia.