In order to elucidate autoimmune B-cell recognition sites of human thyrotropin receptor (TSHR), nine overlapping synthetic peptides (residues 12-30, 24-44, 151-175, 171-195, 308-328, 324-344, 339-364, 359-380, and 375-399) were synthesized and biological activities of antibodies against each of the peptide were examined. It was shown that antibodies against TSHR 12-30, 24-44, 151-175, 171-195, 324-344, and 359-380 had thyroid stimulating antibody activity (TSAb), whereas antibodies against 339-364, 359-380, and 375-399 had thyroid stimulation blocking activity (TSBAb). From these results it was concluded that epitopes where TSH receptor antibodies with TSAb and TSBAb activities are bound are widely located in N-terminal, mid portion, and C-terminal regions.