Effects of acetate and bicarbonate dialysates on tolerance to dialysis have been examined in 30 patients with chronic renal failure (CRF). Symptomatic homeostatic impairment (nausea, vomiting, headache) and cardiovascular instability (tachycardia, arrhythmia, dyspnea) were less common (p less than 0.05) in bicarbonate dialysis. The cardiovascular symptoms correlated with antihypertensive effects of acetate (p = +0.48). Tolerance to ultrafiltration was better with bicarbonate dialysis. Gas chromatographic measurement of blood acetate concentrations in 7 patients on bicarbonate dialysis showed them to be 1.4 +/- 0.31 mmol/l at the beginning of dialysis treatment and 1.7 +/- 0.24 mmol/l at its end (normal, 1.7 +/- 0.14 mmol/l). Of 26 patients on acetate dialysis, 9 patients showed initial and late acetate concentrations of 1.7 +/- 0.26 and 2.5 +/- 0.23 mmol/l, respectively, while in 17 patients an initial concentration of 4.8 +/- 0.32 mmol/l rose to 9.0 +/- 1.1 mmol/l at the end of the treatment (p less than less than 0.01). Dialysis-induced complications had a higher incidence in the latter group (p less than 0.02). Acetate dialysis was poorly tolerated by 65% of the patients. The intolerance was aggravated by myocardial lesions and slow acetate turnover indicated by blood acetate concentrations above 7-8 mmol/l.