An observational study was performed to compare five compounds asinitial therapy to evaluate the persistence with antihypertensivetreatment and drug cost. Over a 1-year follow-up period on the entirepopulation (approximately 360,000 residents) of the Ravenna LocalHealth Unit. The presence of five major antihypertensive agents betweenJanuary 1st, and December 31st, 1997 was investigated. There were4614 patients enrolled. The annual average cost of treatment rangedbetween euro 44.27 (95% confidence interval, 38.18-52.06) for patientsstarted on atenolol to euro175.65 (150.37-205.10) for those startedon losartan. Patients who began losartan showed a higher posteriorprobability of an effective antihypertensive treatment. On average,these patients turned to produce cost-effective treatment with anaverage probability of 0.70.