Transmission EM of CFBE41o- cells transfected at the optimal lipid/DNA ratio (6+/1-) and fixed 5 h after the start of transfection. (A) gold-labelled DNA complex; (B) labelled complexes interacting with cell membrane; (C) a detail of B at higher magnification. ee: early endosome. Arrows indicate endocytosis of the lipid/DNA complex. Bars: 200 nm.