BALB/c mice were immunized with the purified recombinant Hsp A1 protein of Mycoplasma suis.Two hybridoma cell lines secreting MAbs against HspA1 protein were screened by indirect enzymelinked immunosorbent assay(ELISA) and named as 4 B4 and 2 G2,resp.Western-blot results showed that the two MAbs reacted specifically with recombinant Hsp A1 protein.The additive ELISA showed that the two MAbs reacted with the same antigen determinant,and their isotypes both belong to IgG1/k.The ELISA titers of 4 B4 and 2 G2 in supernatant and asicite were 1 : 3 200,1 : 800 and 1 : 13 107 200,1 : 819 200,resp.