Pulsed-field electrophoresis (PFGE) has become one of the most widely used methods for the evaluation of radiation-induced DNA double-strand breaks (dsb). In most studies a simple quantification of DNA migration from the well in the gel has been used as the correlate with dsb formation. Here we have compared such a method, as calibrated with 125I-labelled UdR, with two methods which involved the analysis of the distribution of sizes of DNA fragments migrating in the gel. We conclude that the three methods produce similar absolute values for dsb induction frequency. It is not clear which is the single method of choice but the comparison of the analyses increases the information which can be derived from PFGE experiments.