Eight chronic hemodialysis (cHD) patients and six healthy sedentary controls (C) were exercised for 60 minutes at 52 +/- 8% (cHD patients) and 48 +/- 4% (C) of their maximal oxygen consumption levels. Plasma lactate levels at rest and during exercise were comparable in both groups. Respiratory exchange ratios were lower in cHD patients, but they increased during exercise to levels comparable to those of the C group. Despite comparable heart rates at rest, exercise of similar intensity led to lower heart rates at 30 and 60 minutes in cHD patients compared to C (P less than 0.05). The cHD patients had higher systolic and mean arterial pressures at rest than did C (P less than 0.05), but during exercise the increments in systolic and mean blood pressures were lower in cHD patients than they were in C (P less than 0.05). In spite of these blunted cardiovascular responses, plasma catecholamines increased during exercise in both groups. Plasma glucose levels were similar in both groups during exercise in spite of significantly higher plasma levels of insulin and glucagon in cHD patients throughout the exercise session (P less than 0.01). These data demonstrate that chronic cHD patients can exercise at a modest intensity for a prolonged period of time without untoward cardiovascular or metabolic responses. Their poor exercise response does not appear to be related to an inadequate activation of the sympathoadrenal system.