Chronic renal failure can result in a variety of conditions leading to muscle weakness. However, little is known about inspiratory muscle performance and the acute effects of hemodialysis on the muscles. We investigated the inspiratory muscle performance in chronic renal failure patients undergoing maintenance dialysis. Static inspiratory pressures and inspiratory muscle endurance were determined in 21 patients (13 men and 8 women), before and after dialysis. Inspiratory muscle strength before dialysis was significantly reduced in all subjects but one (mean +/- SEM, PImax = 52.9% of predicted). Following dialysis, the static inspiratory pressure was increased in 18 patients, decreased in 1 patient and remained unchanged in 2. Inspiratory muscle endurance was almost normal before dialysis (mean +/- SEM, PmPeak/PImax = 66.1%). Following dialysis, the inspiratory muscle endurance increased in 13 patients, decreased in 5 patients and remained unchanged in 3. There was no significant correlation between inspiratory muscle strength and the time on chronic hemodialysis. We conclude that in patients with chronic renal failure receiving maintenance hemodialysis there is predialysis reduction in inspiratory muscle strength and less significant reduction in the endurance. Both the inspiratory muscle strength and endurance significantly increased following hemodialysis in most but not all of the subjects. The dialysis-induced changes in biochemical parameters may exert opposing effects on inspiratory muscle performance. This might explain the diversity of the results obtained in this study and studies performed by others.