We have examined a patient with progressive systemic sclerosis (PSS) who had increased serum T3 (235 ng/dl) and T4 (13.2 micrograms/dl) and low 24-h thyroidal 123I-uptake (1.2%). A diagnosis of silent thyroiditis was made on the basis of the clinical course and laboratory and histopathologic findings. Simultaneous measurement of serum anti-thyrotropin receptor antibody (TRAb) showed a negative value (-49.0%) which suggested the presence of anti-TSH antibody. Further examination by immune precipitation with 125I-bovine TSH (bTSH) and also with 125I-human TSH (hTSH) revealed the presence of anti-bTSH antibody but not anti-hTSH antibody in his serum gamma-globulin. The significance of the association of PSS, silent thyroiditis, and anti-bTSH in one individual is discussed.