A follow-up of immunohistological events of Kveim reactions was made by taking biopsies from Kveim test sites at various intervals. Immunoglobulins were present in one half of the specimens taken at 2-7 days, but not earlier. 2-week-old reactions showed immunoglobulins in 50% of the cases and older reactions in 79%. Out of 52 specimens examined with specific conjugates, IgM was demonstrated in 42, IgG in one, and IgA in one reaction. Complement (C3) was seen in 83% out of 47 specimens examined. Complement and immunoglobulins were found in vessel walls but not elsewhere in the tissues.