Methine dyes of the formula ##STR1## where K is a 5- or 6-membered carbocyclic or heterocyclic radical, X is nitrogen or a radical of formula C--Q.sup.1, and Q.sup.1, Q.sup.2 and Q.sup.3 are each independently of the others hydrogen, C.sub.1 -C.sub.6 -alkyl with or without interruption by 1 or 2 oxygen atoms in ether function, benzyl, C.sub.3 -C.sub.8 -cycloalkyl, substituted or unsubstituted phenyl, C.sub.1 -C.sub.4 -fluoroalkyl, C.sub.1 -C.sub.6 -alkoxy, benzyloxy, substituted or unsubstituted phenoxy, C.sub.1 -C.sub.6 -alkylthio, halogen, cyano, formylamino or a radical of the formula R.sup.3, --COR.sup.1, --CO--NHR.sup.1, --CO--NH--CO--R.sup.1, --CO--NH--CO--R.sup.4, --CO--NH--SO.sub.2 R.sup.4, --NH--CO--R.sup.1, --NH--CO--OR.sup.1, --NH--CO--NR.sup.1 R.sup.2, --NH--CSOR.sup.1, --NH--CS--NR.sup.1 R.sup.2, --NH--CO--R.sup.4, --NH--SO.sub.2 --R.sup.1, --NH--SO.sub.2 --R.sup.4 or --NH--SO.sub.2 --NR.sup.1 R.sup.2, where R.sup.1 and R.sup.2 are each independently of the other C.sub.1 -C.sub.13 -alkyl with or without substitution, C.sub.3 -C.sub.8 -cycloalkyl or substituted or unsubstituted phenyl, or else --NR.sup.1 R.sup.2 is amino, R.sup.3 is a nonaromatic heterocyclic radical and R.sup.4 is a heterocyclic radical or Q.sup.1 and Q.sup.2 are together with the carbon atoms to which they are attached a carbocyclic or heterocyclic ring, with the proviso that at least one of Q.sup.1, Q.sup.2 and Q.sup.3 is R.sup.3, are useful in thermal transfer.