Two hundreds mild to moderate hypertensive patients (mean age 54 +/- 10, 115 males, 85 females) were randomised in a multicentre, double blind, two parallel groups trial in order to compare the efficacy of moxonidine (0.2 mg od) and rilmenidine (1 mg od), two selective I1 receptor agonists. The dosage had to be shifted after a four-week treatment period (moxonidine 0.4 mg od or rilmenidine 2 mg bid) if DBP > 90 mmHg. More than half of the patients had to be shifted to a double dose. The blood pressure was normalised (DBP < or = 90 mmHg) for 47% of the moxonidine patient’s and 50% of the rilmenidine patients. The DBP decrease reached 7.3 mmHg in the moxonidine group and 8.0 mmHg in the rilmenidine group (P = 0.28). The SBP decrease was the same in the two groups (7.6 mmHg). Both drugs were well tolerated. The great affinity of moxonidine and rilmenidine for the I1 receptors and the weak affinity for the alpha 2 receptors were probably responsible of the small number of adverse events which are generally linked to the centrally acting antihypertensive drugs (asthenia, somnolence, oedema). Because moxonidine and rilmenidine are often to be prescribed at double dose and are often associated with other antihypertensives, moxonidine whose dosage could be shifted without having to increase the number of daily intakes could enhance the patient’s comfort and make the compliance easier.