SUMMARYPrevious results obtained in our laboratory showed thatnovel class I antigens, closely related to HLA‐A (TM antigen related to HLA‐A9 and GO antigen related to HLA‐A24), were expressed onactivatedHLA‐A9 or HLA‐A24 peripheral blood lymphocytes (PBL), whatever activation factor was used [mitogenic stimulation (PHA, PWM, Con A), EBV transformation or alloactivation], but not on resting T and B lymphocytes. These antigens were also expressed on HLA‐A9 or HLA‐A24 common acute lymphoblastic leukaemias (CALL) and some ‘immature’ chronic lymphocytic leukaemias (B‐CLL), but not in hairy cell leukaemias (HCL), most of the B‐CLL, acute myeloblastic leukaemias (AML) and acute myelomonoblastic leukaemias (AMoL). In order to investigate the regulation mechanisms of these novel class I antigens, PBL and different leukaemic cell types were treatedin vitrowith recombinant IL‐2 (rIL‐2) and α and γ‐interferon (rIFN). Our results showed that without previous activation, but after culture with rIL‐2, TM and GO antigens could be induced in HLA‐A9 or HLA‐A24 PBL and enhanced in HLA‐A9 or HLA‐A24 B‐CLL cases, whereas no expression was found in HLA‐A9 or HLA‐A24 HCL, T‐ALL, AML or AMoL. After culture with rINFs, the expression of TM and GO antigens could be induced on HLA‐A9 PBL andallHLA‐A9 leukaemic cell varieties. Our results support the hypothesis that the expression of class I anti