Cicletanine is a new antihypertensive agent known for being able to stimulate prostaglandin synthesis in vivo and in endothelial cell cultures. The drug was administered to spontaneously hypertensive rats (SHP-SP) whose hypertension was enhanced by a high sodium content diet. Cicletanine prolonged the animals' survival and reduced the severity of histological renal lesions. PGE2, PGI2 and thromboxane A2 assays performed in renal tissues showed a highly significant increase of PGE2 (a prostaglandin involved in the regulation of renin synthesis) in SHR-SP rats treated with oral cicletanine in daily doses of 30 mg/kg. A less significant increase of PGI2 was found in renal tissues, whereas only slight variations in thromboxane concentrations were observed. The favourable therapeutic effect obtained with cicletanine in the treatment of hypertension may be due, at least in part, to the stimulation of PGE2 and PGI2 production in renal tissue.