The effects of conditions-in which nitrile rubber was vulcanized in contact with metallic substrates (e.g. brass or steel)-on the adhesion strength of rubber-substrate joints were investigated. The adhesion strength was estimated by measuring the peel resistance when the metallic foil was separated from the vulcanizate film. When the raw rubber was vulcanized, the plots of 'adhesion strength-versus-vulcanization parameters' (such as temperature and length of the process) show maxima, the pattern (character) of which depends on the substrate material. For joints with steel, the maximum in adhesion strength results from variations in the mechanical properties of the rubber which undergoes transition from the viscous flow to the highly elastic relaxation state in the course of vulcanization. The authors believe that the strength of adhesional bonding in rubber/brass systems depends on the mechanical properties of the sulfide film formed on the substrate in the course of vulcanization of the rubber. Experimental results which support the cohesive nature of the failure in the sulfide film in rubber/brass joints are presented in this paper.