Novel polycyclic guanine derivatives of formula (I) and (I'), wherein J is oxygen or sulfur, R1 is hydrogen, alkyl or alkyl substituted with aryl or hydroxy; R2 is hydrogen, aryl, heteroaryl, cycloalkyl, alkyl or alkyl substituted with aryl, heteroaryl, hydroxy, alkoxy, amino, monoalkylamino or dialkylamino, or -(CH¿2?)mTCOR?20¿ wherein m is an integer from 1 to 6, T is oxygen or -NH- and R20 is hydrogen, aryl, heteroaryl, alkyl or alkyl substituted with aryl or heteroaryl; R3 is hydrogen, halo, trifluoromethyl, alkoxy, alkylthio, alkyl, cycloalkyl, aryl, aminosulfonyl, amino, monoalkylamino, dialkylamino, hydroxyalkylamino, aminoalkylamino, carboxy, alkoxycarbonyl or aminocarbonyl or alkyl substituted with aryl, hydroxy, alkoxy, amino, monoalkylamino or dialkylamino; R?a, Rb, Rc and Rd¿ independently represent hydrogen, alkyl, cycloalkyl or aryl; or (R?a and Rb) or (Rc and Rd) or (Rb and Rc¿) can complete a saturated ring of 5- to 7- carbon atoms, or (R?a and Rb¿) taken together and (R?b and Rc¿) taken together, each complete a saturated ring of 5- to 7- carbon atoms, wherein each ring optionally can contain a sulfur or oxygen atom and whose carbon atoms may be optionally substituted with one or more of the following: alkenyl, alkynyl, hydroxy, carboxy, alkoxycarbonyl, alkyl or alkyl substituted with hydroxy, carboxy or alkoxycarbonyl; or such saturated ring can have two adjacent carbon atoms which are shared with an adjoining aryl ring; and n is zero or one. The compounds of formulas (I) and (I') are useful as antihypertensive, muscle relaxant and bronchodilating agents.