Transfer of genes via DNA virus vectors to human airway epithelial cells is not fully understood. We tested the effects of multiplicities of infection (moi) and incubation time on the efficiency of gene transfer by adenovirus vectors and AAV vectors in cultures of human airway epithelial cells. The cells were exposed to Ad-CMV-lacZ or AAV-CMV-LacZ for 1 to 48 hours at different moi from 0.1 to 100. Efficiency of transduction was assessed as the percentage of cells that expressed LacZ, and was measured by using X-gal staining. A dose-dependent relationship was found between vector moi and the percentage of cells that expressed LacZ. For both vectors, gene expression was greater when incubation time was longer (up to 12 hours), which suggests that the uptake of vectors into the cells is not selective. Efficiency of transduction did not differ between adenovirus and AAV vectors at the same moi. These results suggest that (1) gene transfer via DNA virus vectors increases in a moi-dependent fashion, and that (2) gene expression of the DNA virus vector may be increased by prolonged exposure of the vector to human airway epithelial cells.