The dose dependence of crosslinking yields was determined for irradiated compositions of poly(vinyl chloride) and polyethylene with an allylic polyfunctional monomer (PFM). Therewith, the notion of the differential crosslinking yield G(c)* was used. The dose dependence of G(c)* has a maximum for the investigated systems. The current consumption of allylic groups and PFM molecules was determined. In the investigated systems, the process of network formation proceeds through chain crosslinking of graft chains of poly-PFM.