Systemic changes related to cytokine expression levels in women with endometriosis remain a subject of controversy. There are many studies concerning this topic showing differential serum cytokine levels; however, there are limited data presenting cytokine expression at the single-cell level. This study focused on this question by measuring intracellular cytokine staining of activated peripheral CD3+ and CD14+ cells from women with endometriosis (investigative group) compared with those with uterine leiomyoma (control group). Isolated peripheral blood mononuclear cells from women with endometriosis and uterine leiomyoma were stimulated with PMA and ionomycin or with LPS to induce intracellular synthesis of TNF-alpha, IFN-gamma, and IL-8 in subpopulations of CD3+ cells and TNF-alpha, IL-6, IL-10, MCP-1, and IL-8 in CD14+ cells. Comparison of the total groups of patients showed no significant differences in any of the intracellular cytokines investigated in the T cells and monocytes of women with endometriosis compared with controls. When the group of women with endometriosis was divided with regard to severity of disease, a significantly lower percentage of CD3+CD8- lymphocytes stained for IFN-gamma and a significantly higher percentage of CD14+ cells stained for MCP-1 in advanced endometriosis patients compared with the control group were observed. We conclude that peripheral mononuclear cells in women with advanced endometriosis may have differential cytokine synthesis in vitro. These results support the idea that differing immune cell activity measured by intracellular cytokine profiles in women with advanced endometriosis may be more a consequence of the disease than a cause.