DNA transfection can be too inefficient to establish a desired number of stable transfectants, particularly in lymphocytes; however, this could be circumvented by increasing the absolute frequency of random integration. In this paper, we show that treating cells with topoisomerase II inhibitor following electroporation greatly (approximately 10- to 20-fold) enhances random integration of input DNA in a human pre-B lymphocyte cell line, Nalm-6. With the use of various kinds of topoisomerase II-targeting agents, we also present evidence that topoisomerase IIalpha inhibition is critical for the enhancement of random integration, while the contribution of topoisomerase IIbeta may be negligible. As topoisomerase IIalpha is highly expressed in vigorously growing cells, our results show that topoisomerase IIalpha inhibition provides a promising way of enhancing random integration in virtually all cultured cell lines.