Human colon cancer cells utilize the epidermal growth factor (EGF) family of growth factors and the receptor for these growth factors (EGFR) in sustaining their malignant phenotype. Disrupting EGFR expression by expressing antisense EGFR RNA (through transfection with an appropriate antisense EGFR expression vector under metallothionein promoter control) downregulated the malignant behavior of human colon cancer Moser cells and blocked the ability of exogenous EGF in stimulating malignant cell behavior. The antiproliferative effect of antisense EGFR expression vector was determined in three human colon cancer cell lines (Moser, HCT116 and HT29 possessing different biological properties and rate of proliferation) in an in vitro therapeutic setting using an antisense EGFR expression vector under the control of a viral promoter. Different degree of inhibition was achieved for each cell line after one dose of antisense treatment. The differences in the antiproliferative effect observed may be due to differences in the rate of proliferation and/or recovery from antisense effect, and the differences in transfection efficiency among the cell lines.