The effects of ovariectomy, ovariohysterectomy and hysterectomy on morphologically demonstrable characteristics of lymphoid organs, peripheral white blood cell counts and antibody production against sheep red blood cells (SRBC) were studied in female Lewis rats. Removal of ovaries induced enlarged thymus weight and cellularity. No differences were observed between the groups in spleen weight, while hysterectomy together with ovariectomy influenced relative uterus draining lymph node (UDLN) weight. The percent numbers of pan T, helper T lymphocytes, cytotoxic/suppressor T cells and IgG bearing cells (B lymphocytes) of all investigated organs showed only moderate changes caused by the surgical procedures. In contrast, removal of ovaries generated elevated total leukocyte and lymphocyte counts in peripheral blood. The changes in absolute blood lymphocyte counts were accompanied by similar variations in absolute T and B lymphocyte numbers. Ovariohysterectomy had slightly greater effects on these parameters than ovariectomy alone. In addition, ovaries and uterus had only moderate influences on systemic immune responses toward SRBC. In conclusion, the present results indicate that the removal of ovaries and uterus can modify morphological characteristics of lymphoid organs and peripheral blood but antibody production showed only moderate changes caused by the surgical procedures.