Autoinflammatory phenomena, including autoantibody production and atopy, have been regarded as associated with endometriosis. The present study investigates the activity of eosinophils and the distribution of immunoglobulin E concentrations in the peritoneal fluid of women with early endometriosis. The study group consisted of 30 patients with laparoscopically diagnosed early endometriosis. The healthy control group consisted of 18 females with no evident changes in the abdominal cavity and no endometrial foci. Concentrations of immunoglobulin E in serum and peritoneal blood were determined by enzyme immunoassay. The activity of eosinophils was estimated according to the expression of the early activation molecule CD69 by the flow cytometry method. The concentrations of immunoglobulin E in the peripheral blood and peritoneal fluid were similar in both groups. However, the count of CD69+ eosinophils was higher in the peritoneal fluid of women with endometriosis. The results indicate that activated eosinophils accumulate in the peritoneal fluid in early endometriosis and can play a significant role in the pathogenesis of the disease.