The concentration dependent influence of adenine nucleotides, thrombin and ionophore A 23187 on eicosanoid-production of human endothelial cells was investigated. The prostaglandin I2 (PGI2)-and thromboxane A2 (TXA2)-release were highest at concentrations of 1 mmol/l and 4 mmol/l adenine nucleotides, respectively. TXA2-release decreased at higher concentrations. Ionophore-induced eicosanoid-formation reached its maximum at 15 mumol/l for both PGI2 and TXA2. Thrombin stimulation resulted in a bell shaped concentration dependency, whereby most TXA2 was released at a concentration of 1 U/ml and most PGI2 at 5 U/ml. Intracellular cAMP showed significant (p less than 0.01) increases stimulating cells with ADP- and ATP-concentrations higher than 500 mumol/l, whereas ionophore and thrombin did hardly affect cAMP levels.