This paper is the second devoted to the controlled trial "A.I.C.L.A." comparing aspirin, aspirin + dipyridamole and placebo in the secondary prevention of athero-thrombotic cerebral ischaemic events. It presents the description and distribution of baseline characteristics at entry. Six hundred and four patients (men: 70 p. 100, mean age : 63) were entered. Risk factors were distributed as follows: arterial hypertension: 63 p. 100, Diabetes: 24 p. 100, High blood lipids: 26 p. 100, high uric acid: 20 p. 100, hematocrit greater than 46 p. 100: 34 p. 100, cigarette smoking: 64 p. 100, angina pectoris and myocardial infarction: 15 p. 100, peripheral vascular disease: 7 p. 100, 37 p. 100 of patients had a stroke prior to entry. The ischemic event at entry occurred not more than one year prior to randomization and less than 3 months in 77 p. 100. It was much more often a completed stroke (84 p. 100) than a transient ischaemic attack (16 p. 100) and was referrable either to the carotid (46 p. 100) or the vertebrobasilar circulation (50 p. 100). On the whole patients are older and strokes more severe than in other similar studies. Randomization produced remarkably comparable treatment groups since almost no significant difference was observed between the 3 groups.