Tanned leather, skin or pelt is produced by non-metal tanning, comprising the step of tanning a bated hide, skin or pelt with a tanning agent (A), the tanning agent (A) being a sulfo-group-containing dichloro-diazine selected from compounds of formula (I), (II), (III) and mixtures of two or more thereof, wherein R1 signifies hydrogen, methyl, methoxy, benzoyl, naphthoyl, mono- or di(C1-4-alkyl)-aminocarbonyl, C1-8-alkoxy-carbonyl or oxy-mono- or oligo-C2-3-alkyleneoxy)-carbonyl, R2—(SO3M)n signifies a radical of formula (a) or (b), wherein R3 signifies hydrogen, C1-8-alkyl or C1-8-alkoxy, m is 1 or 2, n is 1 or 2, and M signifies hydrogen or an alkali metal cation or an ammonium cation, the ammonium cation being a protonated tertiary amine or a quaternary ammonium cation, in a tanning bath, the tanning bath having a pH of from 6 to 10 at the beginning of tanning step.