Twenty-four hypertensive patients have been studied. All had blood pressure recordings greater than 160/95 mmHg on 3 occasions whilst taking a beta blocker and two other antihypertensive agents in therapeutic doses. Compliance was checked by intermittent urine analysis for the relevant beta-blocker. These difficult to control hypertensives were treated with nadolol alone, nadolol plus indapamide and nadolol plus xipamide each for 2 months in random order. The aim was to reduce the blood pressure to below 160/95 mmHg. The supine blood pressure on nadolol alone (167/100 mmHg) was comparable to that on the previous three drug regimens (157/100 mmHg), the other two treatments were more effective (145/90 and 148/93 mmHg respectively). Hypokalaemia (serum potassium below 3.5 mmol/l) occurred in six individuals but occurred more frequently on xipamide than on indapamide.