Twenty-four triamines and three tetramines were synthesized. Seventeen triamines inhibited platelet aggregation induced by collagen at a concentration below 10 mumol/L (IC50). Ten triamines in a 100 mumolar concentration inhibited fibrin formation induced by thromboplastin by more then 75%. Both effects do not run parallel. They are strongly dependent from the steric and lipophilic properties of the title oligoamines. The tetramines were nearly inactive.