v-Triazolyl-[4,5-d]-pyrimidines of the formula ##STR1## wherein Q is a mono- or disubstituted amino radical, R is an optionally substituted alkyl or aryl group and the benzene ring A can carry one or two substituents. The compounds are suitable as fluorescent whitening agents for organic material of high molecular weight, especially polyamide. The compounds are obtained by starting from a 4-aminopyrimidine which is correspondingly substituted in the 2- and 6-position, coupling it with the diazonium salt of an optionally substituted aniline and oxidising the resultant azo compound to the triazolylpyrimidine.