Lymph nodes surgically removed from patients with various diseases were histochemically investigated. Enzymes examined were alkaline phosphatase (A1P), acid phosphatase (AcP), β‐glucuronidase (β‐G), and N‐acetyl‐/3‐glucosaminidase (NGa). On the other hand, adult albino rabbits and Wistar rats were immunized by horseradish peroxidase (HrP) mixed with Freund's complete adjuvant and the localizations of these enzymes, antigen HrP and its antibody in their regional lymph nodes at various stages of the immunization were investigated.AIP in the human lymph nodes was mainly localized in the reticulum cells of the paracortical areas in a characteristic network pattern. This pattern was most prominent in the lymph nodes of SLE patients with elevated serum y‐globulin. In the regional lymph nodes of the albino rabbits immunized with HrP, both A1P and anti‐HrP antibody were localized along the processes of reticulum cells in the paracortical areas showing a similar network pattern.Theβ‐Gactivity in the human lymph nodes was very intense and particulated in plasma cells and lymphocytes In the medullary cords and paracortical areas. The proliferation of these β‐G positive plasma cells and lymphocytes in the medullary cords and paracortical areas was most remarkable In SLE patients. In addition, the β‐G activity in these cell types responded most readily and steadily to the antigenic stimulation of HrP to both albino