The kinetics and mechanism of the atom transfer polymerization of styrene initiated with 1-phenylethyl chloride/CuCl/2,2'-bipyridine have been investigated in homogeneous media in the presence of dimethylformamide at 130 degreesC. The results are in agreement with a fisrt-order dependence with respect to CuCl, but an apparent zero-order dependence with respect to the initiator has been observed, contrary to other reports in the literature. This order does not result from side reactions and has been accounted for by assuming a constant value of the [PECl]/[CuCl2] ratio in the range of concentrations investigated. The results do not allow to distinguish between the conventional first-order treatment and that taking into account the persistent radical effect.