Disclosed are thiol dyes of formula (1), wherein R.sub.1 is hydrogen; C.sub.1-C.sub.12alkyl; or phenyl-C.sub.1-C.sub.4alkyl; X is C.sub.1-C.sub.12alkylene; C.sub.2-C.sub.12alkenylene; C.sub.5-C.sub.10cycloalkylene; C.sub.5-C.sub.10arylene; or C.sub.5-C.sub.10arylene-C.sub.1-C.sub.10alkylene; Y is the residue of an organic dye which corresponds to the formula (1a), wherein R.sub.2 is hydrogen; or C.sub.1-C.sub.5alkyl; R.sub.3 is a radical of formula (1a.sub.1): (1a.sub.2); or (1a.sub.3); or R.sub.2 and R.sub.3 together with the linking carbon atom C form a 6 to 10 membered carbocyclic ring which may optionally be a condensated aromatic system and may contain one or more than one hetero atom; and R.sub.4, R.sub.5 and R.sub.6 independently form each other are hydrogen, or C.sub.1-C.sub.5alkyl; Z is H; or a thio ester group of formula (1b), wherein A is O; S; or N--R9; B is --OR7; --NR7R8, or --SR7; and A is O; S; or N--R.sub.9; B is --OR.sub.7; --NR.sub.7R.sub.8, or --SR.sub.7; and R.sub.7, R.sub.8 and R.sub.9, independently from each other are hydrogen; C.sub.1-C.sub.12alkyl C.sub.6-C.sub.12aryl; or C.sub.6-C.sub.12aryl-C.sub.1-C.sub.12alkyl. The compounds are useful for the dyeing of organic materials, such as keratin fibers, preferably human hair.