The present study was an attempt to characterize the type of adenosine receptor in human coronary arteries obtained from organ donors with the use of adenosine analogs. Prostaglandin F2 alpha (10(-6) M) produced tonic contractions followed by phasic contractions and diltiazem (10(-6) M) pretreatment changed the phasic contractions to tonic contractions. Adenosine and its analogs (5'-N-ethyl-carboxamide adenosine, NECA and N6-L-phenyl-isopropyl adenosine, L-PIA), produced concentration-dependent relaxations of the tonic contractions and the order of potency was found to be: NECA greater than L-PIA greater than adenosine. 8-Phenyltheophylline (5 X 10(-6) M) antagonized the relaxations produced by adenosine and its analogs. The data suggest the existence of A2 adenosine receptor in human coronary arteries.