R Re es sp pi ir ra at to or ry y m mu us sc cl le e s st tr re en ng gt th h d du ur ri in ng g c co on nt ti in nu uo ou us s a am mb bu ul la at to or ry y p pe er ri it to on ne ea al l d di ia al ly ys si is s ( (C CA AP PD D) ) N Maximum pressures, spirometry and lung volumes were measured before dialysis, 4 h after the administration of 2 l of dialysate into the peritoneal cavity, and just after the next drainage. In addition, biochemical indices (urea, creatinine, sodium, potassium, calcium and phosphorus) and haematological indices (haemoglobin (Hb) and haematocrit (Hct)) were measured once before the treatment.The results showed that mean PImax and PEmax were normal, with a very wide range between patients, before CAPD. However, seven patients (27%) showed a PImax of <75% predicted (pred) and eight (31%) a PEmax <75% pred. Maximal pressures decreased significantly during CAPD and increased again after the drainage of fluid. Similarly, lung volumes were within the normal range before and decreased significantly during CAPD. The forced expiratory volume in one second to forced vital capacity (FEV 1 /FVC) ratio did not change.We conclude that respiratory muscle strength was preserved in the majority of the patients with chronic renal failure treated with CAPD. During CAPD, lung volumes and respiratory muscle function were decreased, demonstrating an effect of the abdominal cavity on the mechanics of the respiratory system. However, the decrease in the maximum pressures was less than 20%, indicating that CAPD is a safe procedure in patients without pre-existing pulmonary disease or uraemic pulmonary complications. Respiratory muscle strength increased immediately after the drainage of fluid.