Blood pressure stability is better during cold hemodialysis (HD). This has mainly been attributed to a more pronounced sympathetic activation during cold than during warm HD. The authors studied the effect of dialysate temperature on vasoactive peptides, noradrenaline (NA), and renin (PRA). Ten hemodynamically stable patients were dialyzed for 240 min with each of two dialysate temperatures: 38.5 degrees C (warm HD = WHD) and 34.5 degrees C (cold HD = CHD). A decrease (P < 0.05) in blood pressure occurred during WHD; however, during CHD, blood pressure was stable. There were no differences in vasoconstrictors between the two regimens. There was a decrease in NA (P < 0.05), a tendency of PRA to increase (NS owing to a large statistical spread), while arginine vasopressin was unchanged. During CHD, there was a small increase in neuropeptide Y (NPY); however, during WHD, NPY only tended to increase. However, the relative NPY levels (percent of baseline levels) after WHD and CHD did not differ. The vasodilator response was similar during both treatments. Calcitonin gene related peptide was unaltered. Motilin tended to decrease initially, but then increased (P < 0.05) to baseline levels. An increase occurred in beta-endorphin (P < 0.05) and substance P(P < 0.01). There was an initial rise (P < 0.05) in vasoactive intestinal peptide (VIP), followed by a tendency to decrease during the remainder of treatment. The authors concluded that blood pressure stability was better during CHD. However, this was not reflected by differences in plasma levels of the vasoactive peptides, nor did they find any difference in the sympathetic drive between the two regimens.