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The Fab fragment of monoclonal antibody B4G7 against human epidermal growth factor (EGF) receptor was conjugated with cationic poly‐l‐lysine and the resulting conjugate was further complexed with reporter genes or therapeutic genes. This Fab/DNA complex was designated as “Fab immunogene”. The Fab immunogene transfer in vitrowas mediated through the EGF receptors in two melanoma cell lines. The frequency of cells expressing β‐galactosidase (β‐Gal) reporter gene was approximately 1%. The induction of suicide effects after Fab immunogene transfer of herpes simplex virus thymidine kinase (TK) or Escherichia colicytosine deaminase (CD) gene was quite remarkable, and the growth of melanoma cells was inhibited for over 7 days in the presence of ganciclovir (GCV) or 5‐fluorocytosine (5‐FC). Similarly, when melanoma cells treated in vitrowith the Fab immunogene carrying TKor CDwere transplanted into the back of nude mouse, subsequent systemic administration of GCV or 5‐FC effectively suppressed the growth of tumors, indicating the occurrence of in vivosuicide effects.