This invention relates to novel triazolopyrimidine derivatives of formulae (Ia) and (Ib), ##STR1## wherein Q represents hydrogen, a heterocyclic group optionally substituted by a C.sub.1-4 alkyl group and containing one or more oxygen and/or nitrogen atoms or a group of formula--SR.sup.1 wherein R.sup.1 is alkyl or aralkyl, or a group of formula--NR.sup.2 R.sup.3 wherein R.sup.2 and R.sup.3 are independently hydrogen, alkyl, alkenyl, cycloalkyl, aralkyl, aryl or a heterocyclic group,m and n are independently 0, 1, 2, 3 or 4, with the provision that if m stands for 0, then n is different from 0, and if both n and m are 1 or m stands for 0 and n is 2, the Q is different from methylthio or morpholino group, their mixtures or pharmaceutically acceptable salts. Furthermore, the invention relates to a process for preparing these compounds.The compounds of formulae (Ia) and (Ib) are able to inhibit the ptosis caused by tetrabenazine and they have analgetic activity.