3-Deazaguianines of formulae Ib and inters. Ia are new together with their acid-addn. salts (where X is NH -NH2 or -OMe; Y is CNHR, CNR' or -CN; R is H or acyl; R' is =CH.NME; Z is H, tetrahydropyranyl beta-D-ribofuranosyl, 5-deoxy-beta-D-ribofuranosyl, beta-D-ribo-furanosyl-5-phosphate, cyclic beta-D-ribofuranosyl-3,5-phosphate, 1-18C acyl and isopropylidene, 1-18C acyl and isopropylidene-5-deoxy-beta-D-ribofuranosyl, 1-18C acyl and isopropylidene-beta-D-ribofuranosyl-5-phosphate or 1-18C acyl-beta-D-ribofurnosyl-3,5-cyclic phosphate; provided that X is NH and Y is C.NHR or CNR and only if X and Y are bound, and X is NH2 or -OMe and Y is -CN only if X and Y are not bound). Cpds. of formulae (where Z is beta-D-ribofuranosyl-5-phosphate, 5-deoxy-beta-D-ribo-furanosyl, ribofuranosyl-3,5-cyclic phosphate, H, tetrahydropyranyl or beta-D-ribofuranosyl) are specif. claimed.