Nonextruded dispersions and concentrates of additives on olefin polymers

A dispersion of one or more additives to be used in the processing of olefin polymers or copolymers, said dispersion comprising nonextruded particles of olefin polymers containing at least two immiscible polyolefinic phases and having internal voids partially or totally filled by the said additive or additives, wherein the amount of additive or additives present in the said internal voids is from 0.5 to 25% by weight, preferably from 0.5 to 20% by weight, with respect to the total weight of the dispersion.