Mammalian genome characterization and biotechnology each require the mobilization of large DNA segments to produce transgenic animals. We recently showed that mouse metaphase II (mll) oocytes could efficiently promote transgenesis (mll transgenesis) when coinjected with sperm and small (< 5 kilobases) ubiquitously expressed transgenes (tgs)(1). We have extended this work and now report that mll transgenesis can readily be applied to a range of larger tgs (11.9-170 kilobases), including bacterial and mammalian artificial chromosome (BAC and MAC) constructs. The efficiency of large-construct mll transgenesis was at least as high as that with small constructs; 11-47% of offspring carried the large tgs. More than 95% of these transgenic founders transmitted the tg to offspring. These data demonstrate the ability of mll transgenesis to deliver large tgs efficiently.