AbstractA study was conducted to determine the incidence and extent to which anorexia, a decrease in spontaneous food intake, contributes to the occurrence of cancer cachexia. Data for ten male subjects with small cell carcinoma of the lung are reported for a five‐month period following diagnosis. Although body weights of the subjects at the time of diagnosis averaged less than 95% of the usual weight (weight 6 months prior to diagnosis), they were greater than 109% of the mean ideal weight. At five months, the mean weight (N = 8) was 88% of the preillness weight. From the time of diagnosis, there was a mean loss of 7.2 kg (15.8 lb). The urinary creatinine excretion was below the normal range, whereas the urinary urea nitrogen values were within the normal range. At the time of diagnosis, the mean triceps skin‐fold measurements were approximately 80% of the standard reference for males.During the five‐month period, the mean midarm muscle circumference determinations remained greater than 90% of the reference standard. The mean serum transferrin values were 10% or more below the reported lower range of normal, whereas the great majority of the serum albumin values were 3.0 gldl or above during the five‐month period. The mean caloric intake of 2,204 kcal at the time of diagnosis was only 86% of the estimated basal energy expenditure (BEE) times a factor of 1.5 used to account for moderate activity. Four months following diagnosis, the mean caloric intake had fallen to 1,702 kcal, only 67% of the BEE×1.5 (calculated from the weight at diagnosis). The findings provide evidence of a decline in spontaneous food intake, a small decrease in body fat, and a greater than 13% weight loss. The oral intake was less than adequate for any activity beyond the basal state. Decreased intake could account for most of the weight loss observed in the subjects.