Thus, tumours (Schisselbauer et al, 1990) or cell lines (Tew, 1994; Hayes and Pulford, 1995) show an increased GST level after development of drug resistance, cancer cells transfected with GSTs can express a drug resistance (Moscow et al, 1989; Manoharan et al, 1991; Morrow et al, 1998; Depeille et al, 2004) and the inhibition by antisense (AS) gene of endogenous GSTP expression reduces drug resistance (Ban et al, 1996). This evidence concerns the gene GSTP1 and neoplasm.