A process for the catalytical preparation of condensation products of formaldehyde, in which formaldehyde or a formaldehyde-forming compound is caused to undergo reaction using a catalyst which has been produced, in the presence of an auxiliary base, from a triazolium salt of formula I ##STR1## in which R.sup.1 and R.sup.3 are the same or different and stand for aliphatic groups having from 1 to 30 carbon atoms, optionally substituted aryl groups, optionally substituted aralkyl groups, and/or optionally substituted heteroaryl groups,R.sup.2 represents hydrogen, the hydroxymethylene group --CH.sub.2 OH or the hydroxy-hydroxymethylene-methylidyne group --CH(OH)(CH.sub.2 OH), andR.sup.4 denotes hydrogen, a halogen atom, a nitro or cyano group, an aliphatic group having from 1 to 30 carbon atoms, an optionally substituted aryl group, an optionally substituted aralkyl group, an optionally substituted heteroaryl group, an alkoxy group --OR.sup.5, a thioether group --SR.sup.6, an amino group --NR.sup.7 R.sup.8, an acyl group --COR.sup.9 or an ester group --COOR.sup.10, where R.sup.5, R.sup.6, R.sup.7, R.sup.8, and R.sup.9 stand for radicals such as those stated above for R.sup.1, and R.sup.10 is a C.sub.1 -C.sub.30 alkyl group or an optionally substituted aryl or aralkyl group, orR.sup.3 and R.sup.4 together form a C.sub.3 -C.sub.5 alkylene or C.sub.3 -C.sub.5 alkenylene group or a C.sub.6 -C.sub.14 arylene group, or a C.sub.7 -C.sub.14 aralkenylene or C.sub.8 -C.sub.14 aralkenylene bridging member, andA is the equivalent of an anion having one or more negative charges for electrical neutralization of the charge on the triazolium cation.