An animal model was developed, permitting the study of thromboxane A2 and prostacyclin neoformation, after arachidonic acid (AA) injection. Two types of physiopathological responses were observed, according to the rabbit strains. In the first type, prostacyclin neoformation was predominant, AA injection inducing only reversible hypotension. In the second type, thromboxane A2 neoformation was prevalent, AA injection inducing irreversible hypotension, marked myocardial troubles, shock, and death. In both types, injection of cicletanine (5 x 10(-5) mole/kg) significantly enhanced prostacyclin neoformation. After cicletanine, a new hypertensive drug, rabbits of the second type responded like those of the first type, without severe physiopathological responses to AA injections.