Vinyl acetate (VAc), styrene (St), and methyl methacrylate (MMA) were irradiated in dilute solution at an absorbed dose rate of 0.5 Mrad/hr in the absence of oxygen at room temperature. In homogeneous systems, telomers are formed with a rate ∝ [M]1 at monomer concentrations [M] > ca. 0.4M. The chain length (D.P..n) increases with increasing [M]. (D.P..n)−1 depends over large ranges of [M] linearly on the ratio [S]/[M] (S = solvent) in accordance with the Mayo equation. These findings were obtained with VAc in methanol and with St in cyclohexane. In heterogeneous systems, telomer is formed at all monomer concentrations. The 100-eV yield for telomer formation passes a maximum of GT(–M) = 40 (MMA in 2-propanol) and GT(–M) = 27 (MMA in cyclohexane) at the onset of polymer formation ([M] ∼ 3 vol-%). With the system St/2-propanol, GT(–M) ∼ 15 was found being independent of [M]. The molecular weight Mn (telomer) increased from ca. 600 to ca. 1200 by increasing [M] up to 100 vol-% (MMA/2-propanol). Mn (telomer) does not depend on [M] in the other two cases (Mn ∼ 500, MMA/cyclohexane; Mn ∼ 700, St/2-propanol).