A linear relationship between the elastic modulus of polymer networks and the transverse relaxation rate of protons attached to the unconstrained polymer is established by considering poly(dimethylsiloxane) (PDMS) chains, cross-linked at random according to two different ways. Networks of type A were composed of long poly(vinylmethyl-dimethylsiloxane) copolymers. With randomly distributed vinyl functions (molar fraction of vinyl functions : 2 x 10(-3) per monomeric unit), links were formed between vinyl and methyl groups, at 150 degrees C; then, networks were quenched at 0 degrees C, during the gelation process. Networks of type B were composed of vinyl-terminated PDMS chains and poly(methylhydrosiloxane-dimethylsiloxane) copolymers, with additional hydride-terminated PDMS chains (molar fraction of hydride functions : 10(-2) per monomeric unit). For these systems, measurements of the storage modulus or of NMR were performed, in situ, during the gelation. This study extends the NMR-swelling interrelationship to the property of elasticity.