After primary successful PTA, 199 patients were randomized into one of three treatment groups, namely, placebo or a combination of 75 mg dipyridamole with either 330 mg (high dose) or 100 mg (low dose) acetylsalicylic acid (ASA) tid. The duration of treatment was six months. Of the 199 patients admitted to the study, 156 completed the six-month trial period. Not all patients had a second angiogram, and in these cases clinical findings were used in the evaluation. Evaluation of the combined angiographic and clinical results showed improvement or no deterioration in 37% of patients in the placebo group compared with 49% in the low-dose and 61% in the high-dose ASA groups respectively. The only statistically significant difference observed was between the placebo group and the group treated with dipyridamole and high-dose ASA (p = 0.01). This difference remained statistically significant at p = 0.039 if only the angiographic findings were considered for group comparison. It cannot, however, be concluded from this study that 75 mg dipyridamole in combination with 100 mg ASA tid is more effective in preventing reocclusion after PTA than in combination with 330 mg ASA tid.