As hypertension often precedes renal failure in polycystic kidney disease, it has been suggested that efficient blood pressure control could slow down the progress of the disease. To test this hypothesis, we made a retrospective study of 32 hypertensive patients with familial polycystic kidney disease who had been followed up for an average period of 75 months (range: 20 to 168 months). We examined the relations between creatinine levels or the slope for their increase with time on the one hand, and the mean blood pressure measurements recorded during the surveillance period on the other hand. For the group of 32 patients as a whole, there was no significant correlation between creatinine levels or their variations and blood pressure or its variations. The 13 patients whose creatinine levels rose by more than 50 p. 100 did not differ from the 19 others as regards age, known duration of hypertension, initial or final blood pressure or the number or nature of the antihypertensive drugs they received. This preliminary investigation does not rule out the existence of a link between blood pressure control and the maintenance of renal function during polycystic kidney disease complicated by hypertension, but it does suggest that any such link is tenuous.