Three cases, in which the deterioration of blood pressure control was associated with the onset of therapy with nonsteroidal anti-inflammatory drugs (NSAIDS), are reported. It is suggested that this effect of the NSAIDs could possibly have resulted from the inhibition of the biosynthesis of the prostaglandins, some of which have vasodilatory or natriuretic properties. This interaction, hitherto unreported from our environment and therefore not commonly recognised, is of relevance in the drug treatment of hypertension since the widely used NSAIDs have the potential to impair the effectiveness of several antihypertensive drugs. It should be taken cognizance of when using both antihypertensive drugs and NSAIDs in any hypertensive patient.