These results support the hypothesis that hyperuricaemia due to treatment of hypertension with chlorthiazide and ganglion-blocking agents is drug-induced and not related to alteration of glomerular filtration caused by a fall in blood-pressure. In our series 15 of the 22 patients achieved a satisfactory mean fall in blood-pressure without a significant rise in the serum uric acid. Although the conrtrol of hypertension is easier using thiazide diuretics with guanethidine (Hilden, 1960;Jaquerod and Spuehler, 1960;Blanchard and Essigman, 1961), the possible danger of prolonged hyperuricaemia causing further renal damage in hypertensives, as is found in patients with primary hyperuricaemia, has to be considered. It may be better to continue with guanethidine alone. and reserve the thiazide diuretics for patients proving resistant to guanethidine, for the latter at present appears to be free from the danger of causing hyperuricaemia. A prolonged study, comparing guanethidine alone and in combination with the thiazide diuretics, is required.