A specially prepared olive leaf extract (EFLA 943) has been tested for its blood pressure lowering activity in rats rendered hypertensive by daily oral doses of L-NAME (NG-nitro-L-arginine methyl ester, 50 mg/kg) for at least 4 weeks. Oral administration of the extract at different dose levels at the same time as L-NAME for a period of 8 weeks showed a dose dependent prophylactic effect against the rise in blood pressure induced by LNAME, best effects being induced by a dose of 100 mg/kg of the extract. In rats previously rendered hypertensive by LNAME for 6 weeks and then treated with that dose of the extract for a further 6 weeks without discontinuation of LNAME, normalisation of the blood pressure was observed. The findings confirm previous reports on the hypotensive