Prevalence and characteristics of nutritional depletion were established by body composition measurements in 255 COPD patients in stable clinical condition admitted to a pulmonary rehabilitation center. Depletion of body weight, fat-free mass (using bioelectrical resistance measurements), and muscle mass [from creatinine height index (CHI) and midarm muscle circumference] was most pronounced (40 to 50%) in patients suffering from chronic hypoxemia and in normoxemic patients with severe airflow obstruction (FEV1 < 35%) but also occurred in +/- 25% of patients with moderate airflow obstruction. Classification of the patients in four groups by body weight and fat-free mass revealed that depletion of fat-free mass may occur in normal-weight COPD patients (Group 3). These patients also exhibit a decreased CHI (61 +/- 21%, mean +/- SD) and suffer from physical impairment (12-min walking distance, WD, 532 +/- 152 m) to an even greater degree than underweight patients with relative preservation of fat-free mass (Group 2) (CHI = 73 +/- 16%; WD = 744 +/- 233 m). No systematic differences were established between the four groups in serum protein concentrations or medication use. We conclude that fat-free mass is a better indicator of body mass depletion than body weight. Classification of COPD patients by body weight and fat-free mass may have consequences for planning and interpretation of intervention strategies, particularly in Group 2 and 3 patients.