Eleven patients with hypertension and varying degrees of stable renal functional impairment were treated with the beta adrenoreceptor blocking drug, acebutolol (Sectral). Parameters of renal, cardiovascular and respiratory function were measured immediately prior to treatment and again after four and 12 weeks. In five patients the blood pressure was well controlled throughout the 12-week period on 400mg of acebutolol each morning, in three the blood pressure was satisfactory after four weeks treatment with 400mg each morning but control had been lost by 12 weeks, while in the remaining three patients 800mg each morning was ineffective. There was no significant change in the mean glomerular filtration rate of the 11 patients but in two of these patients with severe, but stable, chronic renal failure the introduction of acebutolol was associated with a decline in renal function and the onset of uraemic symptoms. One of these patients showed an improvement when the acebutolol was discontinued but the other required regular dialysis treatment. Beta adrenoreceptor blockers should be used cautiously in severe renal failure.