controlled release compositions releasing an effective amount of biologically active material such as pesticide into the environment over an extended period of time are disclosed . the compositions comprise an intimate admixture of an organic polymer and a component incorporating a biologically active material wherein the biologically active material is released by molecular diffusion through the matrix of the polymer at the surfaces exposed to the environment . the component including the biologically active material is incorporated in the polymer in amounts sufficient that diffusion of the component at the surfaces exposed to the environment results in loss of structural integrity and / or fraction of the polymer to thereby expose new surfaces to decomposition for further release of the biologically active material resulting in a rate of release over an extended period of time in proportion to that necessary to offer protection .