Based on our hypothesis that CD26 expression influences tumour cell biology and potentially its sensitivity to cytotoxic treatments, as suggested by previous work showing that CD26 expression is associated with changes in tumour cell line behaviour in vitro and that the clinical behaviour of selected tumours may be correlated with differences in CD26 expression (Morrison et al, 1993; Carbone et al, 1995), we initiated studies using stable CD26 Jurkat transfectants to investigate the effect of CD26 on tumour sensitivity to selected antineoplastic agents. The gene discussed is DPP4; the disease is neoplasm.