Cell-specific productivity was compared in Chinese hamster ovary cell clones transfected at confluency versus subconfluency. Following lipofection of a pCDNA1-derived vector encoding a proteinA-fucosyltransferaseIV fusion protein, selection and single cell sorting by flow cytometry, clones were expanded to tissue flasks and assessed for cell specific productivity. The probability of obtaining high producers at confluency was significantly higher from cells transfected at confluency than at subconfluency (P=0.05).