An acute test was run on healthy volunteers to assess the effect of i.v. dihydroergocristine methansulphonate on platelet function. The number of platelets was virtually unaffected, whereas adhesion to glass was significantly reduced. A direct and specific effect was noted on the 1st, adrenaline aggregation wave, while the 2nd wave (expression of ADP) induced aggregation did not appear to have been significantly altered. It is felt that further examination of the alpha-adrenergic block induced by the drug should be under-taken in view of the recent literature data which explain the inability of commonly employed anti-aggreganting drugs, such as acetylsalicylic acid, to prevent and treat atherothrombosis, in spite of the encouraging experimental results.