A hybridoma cell line(B10)was established by fusing spleen cells of BALB/c mou- se immunized with human thyroglobulin(HTG) with SP2/0 myeloma cells. An averagefusing rate of 6.3% and antibody-secreting positive well rate of 58.3% were obtained.During the first two months, the supernatant of B10 culture had a titer of 1/128 to1/2048 measured by hemagglutination method, and the ascites was positive at 1/64000-128000 and 1/320000 respectively as measured by hemagglutination and radioimmunoass-ay.The B10 cell line is very stable and has very high activity to produce anti-HTGmonoclonal antibodies. After several times of preservation in liquid nitrogen andpassage in culture for one year,a recent determination shows that cell culture super-natant and ascites still have very high titer,being 1/4096 and 1/1048576 respectively asmeasured by hemagglutination method. The chromosome number of the B10 hybridomacell is 99.5?7.4.The success of the establishment of this cell line is briefly discussed.Attempt to establish diagnostic kit with this monoclonal antibody is being undertaken.