Objective: To evaluate the role of local immunity in women with minimal endometriosis. Methods: Uterine endometrium and endometrial implants were obtained simultaneously from 30 infertile women with minimal endometriosis and examined immunohistochemically using antibodies of T cell, B cell, macrophage, Langerhans cell, immunoglobulin (Ig)G and complement (C) 3d. Serum IgG, IgA, IgM, C3, C4, antinuclear antibody and anti-DNA antibody were also examined in 24 of the women. Data from uterine endometrium and serum were compared with 10 fertile women without endometriosis as a control. Results: Microscopic examination revealed that the endometrial implants were divided into two groups: group 1 (n = 13) showed lymphocytic infiltration in the endometrial implants and group 2 (n = 17) showed no or slight lymphocytic infiltration. The endometrial implants of group 1 showed significantly more dense T-cell infiltration than those of group 2. Other types of infiltrating cells and deposits of IgG and C3d revealed no significant differences between groups 1 and 2. The immunohistochemical examination of the uterine endometrium and the serum data revealed no significant differences among all three groups. Cumulative pregnancy rates showed no significant difference between groups 1 and 2. Conclusion: The difference of local immune response in endometrial implants did not affect systemic immunity.