Abstract 1. The adhesion of fractions of NBR of varying polarity to a polyamide has been investigated at room and elevated contact temperatures. 2. The adhesion of each copolymer investigated has been shown to fall with the increase of molecular weight of fractions up to a certain limit (300,000– 350,000). Above this weight the magnitude of adhesion remains practically constant. 3. The adhesion of all fractions tested increases with increasing contact temperature, attaining the cohesive strength of the respective fraction. The lower the value of molecular weight, the lower is this temperature limit. 4. It was shown that at room contact temperature adhesion of nitrile co-polymers to polyamide depends only slightly on the polarity of the adhesive. The lower the polarity of the copolymers, the more the heating of the bonded specimens increases the adhesion strength. The lower adhesion of the polar nitrile copolymers to the highly polar polyamide might be explained by a purely kinetic factor, that is, the lack of flexibility of macromolecules of such polymers and the greater number of intermolecular links, which makes diffusion difficult. 5. It has been established that for bonding at room temperature the adhesion of unfractionated commercial nitrile rubbers to polyamide is determined primarily by the polydispersity of the rubber rather than by its polarity. The adhesion of copolymers at elevated temperatures depends to a high degree on their polarity. 6. It was found that the adhesion of fractions of NBR to nonpolar substrates (PIB) is very low and is independent of polarity and molecular weight, and of temperature of thermal treatment. Smaller values of adhesion in this case are determined by noncompatability of polar adhesive with nonpolar substrates. 7. The results of the work were discussed in the light of the diffusion theory of adhesion.