Obecfive To study the clinical significance of detecting serum proeollagen type Ⅲ(PCⅢ) and hyaluronie acid(HA)in patients with autoimmune thyroid diseases(AITD).Methods According to the thyroid function,the 114 patients with AITD were divided into hyperthyroidism group(38),hypothyroidism group(35),and sub-hypothyroidism group(41).In addition,40 healthy persons were served as controls.The level of serum PCⅢ was determined with ELISA and that of serum HA with RIA.The level of FT3,FT4 and sTSH were detected by immumnofluorometric assay.Results Serum FT3(18.35±6.19)pmol/L]and FT4[(76.28±23.49)pmol/L]level of patients with hyperthyroidism were obviously higher than those of the controls[(4.75±0.31),(16.12±3.27) pmol/L],but serum sTSH[(0.15±0.07)mU/L]was obviously lower than that of the control[(3.78±0.15)mU/L],the differences were statically significant(P＜0.01).Serum FT3[(3.36±0.26)pmol/L]and FT4 [(6.37±2.19) pmol/L]level of patients with hypothyroidism were both lower than those of the controls(P＜0.05).but serum sTSH[(44.58±13.29)mU/L]was obviously higher than that of the control(P＜0.01).Serum FT3 [(4.86±0.45)pmol/L]and FT4[(15.26±2.78)pmol/L]level of patients with sub-hypothyroidism had no statistical difference compared with those of the controls(P＞0.05),but serum sTSH[(14.26±4.73)mU/L] was obviously higher than that of the controls(P＜0.01).The level of sernm PCⅢ[(4.63±1.22)μg/L]in pafients with hyperthyroidism was significantly higher than that of any other group(P＜0.05).There waB no statistical significant difference in PCⅢ among the patients with hypothyroidism,the patients with sub-hypothyroidism and controls [(3.64±1.12),(3.54±1.17)and(3.56±1.07)μg/L],respectively(P＞0.05).The level of serum HA [(31.13±10.28)μg/L]in patients with hypothyroidism was significantly higher than that of any other group(P＜0.05).There was no statistical significant difference in HA among the patients with hyperthyroidism,the patients with sub-hypothyroidism and controls[(22.24±7.22),(22.43±7.99)and(23.09±9.19)μg/L,respectively,P＞0.05].Conclusions It is very significant to understand myocardial fibrosis early through detecting sernm PCⅢ in patients with hyperthyroidism.Measurement of serum PCⅢ and HA will be useful to discovery hepatic fibrosisearly in patients with a long course of hyperthyroidism.