Pulmonary function tests were performed immediately before and after hemodialysis in 11 normovolemic patients with chronic renal failure. In order to delineate the relative contributions of thoracic and abdominal musculature to the breathing process, lung volumes were determined in the horizontal (0°) and semi-upright postures (75°). Maximal static inspiratory and expiratory pressures, hand-grip pressures, flow rates, and arterial blood gases were also determined. Vital capacity, inspiratory capacity, and expiratory reserve Volume were significantly reduced and residual volume was significantly increased in both positions prior to dialysis (relative to predicted values). Maximal static inspiratory pressure, maximal static expiratory pressure, and arterial oxygen tension were also significantly reduced. After dialysis, expiratory reserve volume decreased significantly and residual volume increased significantly in the relative, had a significant prognostic value.