Angiogenesis and inflammation are pivotal processes in developing endometriosis in the peritoneal cavity. The aim of the present study was to evaluate these two processes in women with endometriosis who had been treated with danazol to determine the sensitivity of a non-invasive test in diagnosing endometriosis. The clinical follow-up study was conducted in a group of 103 women diagnosed laparoscopically with endometriosis. Thirty-five patients qualified for danazol treatment. Pain was assessed using a visual analogue scale, whereas endometriosis was assessed using the revised American Society of Reproductive Medicine (rASRM) scale. Cancer antigen (CA)-125 and C-reactive protein (CRP) concentrations in plasma and peritoneal fluid were determined by immunoenzymatic methods, whereas vascular endothelial growth factor (VEGF) and interleukin (IL)-1β concentrations in plasma and peritoneal fluid were determined by ELISA. Endometrial expression of IL-8 and platelet-derived growth factor alpha polypeptide (PDGF-A) was determined using real-time polymerase chain reaction (PCR). Women with endometriosis (68.9% of patients) had higher plasma concentrations of CA-125, as well as higher concentrations of both CA-125 and VEGF in the peritoneal fluid. Endometrial expression of IL-8 mRNA was significantly higher, whereas that of PDGF-A was significantly lower, in contrast. After danazol treatment the patients reported lower pain scores; in addition, CA-125 concentrations in the plasma were decreased (P<0.001), whereas VEGF concentration in the plasma increased (P=0.009). For the diagnosis of endometriosis, none of the combinations of given markers had a sensitivity >60%. Danazol treatment is highly effective in relieving pain and decreasing CA-125 concentrations in the plasma. Higher plasma concentrations of VEGF after treatment could imply stimulation of angiogenesis.