Abstract: Diamino-1,3-5-triazinylstilbene compounds of the formula ##STR1## in which R.sub.1 and R.sub.2 may be identical or different and represent each hydrogen or non chromophoric radicals selected from the group consisting of fluorine or chlorine atoms, phenyl, alkyl, lower alkoxy, lower dialkylamino, lower trialkylammonium, acyl amino or optionally functionally modified carboxy or sulfo groups, or two vicinal radicals, R.sub.1 and R.sub.2 denote together lower alkylene, a fused benzo ring or 1,3-dioxypropylene, the rings A and B having optionally further non chromophoric substituents, and X is O or S.These compounds are good optical brighteners and are prepared by reacting a 4'-cyano-4-benzoxazolyl- or 4'-cyano-4-benzthiazolylstilbene compound with dicyanoamide or with urea and ammonia.