Abstract: Levels of tear and serum β2-MG are determined with radioimmunoassay in 35 patients with herpes simplex keratitis and 40 normal subjects. The results show that tear β2-MG levels of patients with herpes simplex keratitis (13. 21±6. 15 mg/1) and normal subjects (8. 43±1. 52 mg/1) are significantly different(P<0. 01); there is significant difference between β2-MG levels of tear and that of serum in normal subjects (P<0. 001);also significant difference between β2-MG levels of tear and that of serum in patients with herpes simplex keratitis (P<0. 001); no difference between serum β2-MG levels of patients with herpes simplex keratitis and that of normal subjects (P>0. 05). The β2-MG levels of tear is higher than that of serum in normal subjects which reflects more correctly immune condition of patients with herpes simplex keratitis than that of serum.