The kinetics of the second step in the formation of a dis-azocompound from 4, 4′-bis-diazobiphenyl (bisdiazotized benzidine) with 2-naphthol-3, 6-disulfonic acid have been investigated in the presence of various concentrations of urea up to 6,6 M in aqueous buffers. The catalytic action of urea is due to a disaggregation of the diazonium ion aggregates, a base catalysis and a dielectric medium effect.