In order to evaluate the effect of triflusal (2-acetyloxy-4-trifluoromethyl benzoic acid), an orally active antiplatelet agent, on arteriosclerosis progression, a pilot, parallel, double-dummy, double-blind clinical trial vs acetylsalicylic acid (ASA) was carried out in patients with subclinical atherosclerotic lesions. The trial consisted of a 2-week run-in placebo phase, followed by a 12-month oral treatment with triflusal (600 mg/day) or ASA (300 mg/day). The primary variable was identified in the ultrasonic biopsy (UB) score; the secondary variables were the UB class changes of each arterial site, the rate of progression (ROP), the intima-media thickness (IMT), and the symptoms of arteriosclerosis. Data were evaluated by use of analysis of variance and Chi-square test. Forty-three patients (31 men, 12 women, mean age 62.8 +/- 8.4 SD) were randomized to triflusal (15 men, 6 women, mean age 64.3 +/- 6.7) or to ASA (16 men, 6 women, mean age 61.3 +/- 9.6). The analysis of variance on the UB score showed no difference between treatments: the patients' UB scores remained unchanged with no progression, thus indicating that no patient worsened during treatment. When all arterial sites under evaluation are considered, 86% of the sites in the triflusal group and 85% in the ASA group remained unchanged. No relevant change was recorded in vital signs and routine laboratory tests. Gastric disturbances were reported by two and three patients treated with triflusal and ASA, respectively. In conclusion, triflusal appears as effective as ASA in slowing arteriosclerosis progression.