Objective To investigate the effect of thermochemotherapy with 5 fluorocytosine(5 FC) on human colorectal carcinoma cell lines SW480 transfected with carcinoembryonic antigen (CEA) tissue specific cytosine deaminase (CD) in vitro.Methods Recombinant retroviral vector G1CEACDNa, in which CD gene was controlled under the CEA promoter, was introduced through liposome technique to the human colorectal carcinoma cell line SW480, and then the cells were selectively cultured in G418. The proliferated colonies were treated with the combined therapy of 5 FC and hyperthermia at a 43℃ over 30 min for 3 times. RT PCR was performed to analyze the expression of CD gene in target cells after thermochemotherapy. Results The CD gene expressed steadily in the target cells after 3 times of hyperthermic treatment. After the transfection of CD gene, SW480 CEACD cells were more sensitive to 5 FC than their parental cells (P