Protein calorie malnutrition is being recognized with greater frequency in the hospitalized patient. This report describes the clinical presentation and response to nutritional therapy in nine elderly malnourished patients ranging from 73 to 95 years. Clinical features of malnutrition include weight loss, confusion, hypoalbuminemia (mean 2.8 gm/dl), a low total iron binding capacity (TIBC) (mean 192 micrograms/dl), anergy, lymphocytopenia (mean 1×10(3) cells/microliter) and an anemia (mean 9.0 gm/dl). Our subjects were followed for 42 days. In two, hyperalimentation was achieved by voluntary food intake and polymeric dietary supplements. In seven, feeding for 21 days via nasogastric tube was required. After three weeks, weight gain, decreased confusion, improved appetite and mobility, and significant increases in serum albumin and TIBC were seen. At that time, no subject was anergic and lymphocyte counts increased significantly. Increase in the serum iron and percent saturation was noted, and by day 42, a significant elevation in the hemoglobin occurred. As a measure of stem cell function, the committed granulocyte/macrophage progenitor cell (CFU-C) was quantitated in four subjects prior to and following 21 days of nutritional support. A marked increase in CFU-C number from a mean of 0.1×10(7) cells/kg to a normal value of 0.85×10(7) cells/kg was seen. Thus in addition to correcting the nutritional deficit, hyperalimentation returned immune and hematopoietic abnormalities to near normal levels. While improvement could reflect recovery from an associated disease, it is just as likely that correction of malnutrition, a well-recognized cause of these immunologic and hematopoietic abnormalities, accounted for the response. These observations emphasize the importance of recognizing malnutrition in the elderly and highlight the need for a careful nutritional assessment prior to ascribing hematologic and immunologic abnormalities to the aging process.