PURPOSE To present a rat model of subcutaneous endometriosis for the study of pathophysiology and the effects of drugs. METHODS Fifty three-month-old female Wistar rats (Rattus norvergicus) were distributed into one control group and four treatment groups: estradiol (2.5; 5; 10 mg/kg s.c.), medroxyprogesterone acetate (0.5; 2; 5 mg/kg s.c.), triptorelin pamoate (0.18; 0.56 mg/kg s.c.) and acetylsalicylic acid (3 mg/kg per os). The animals were autoimplanted subcutaneously with 4x4-mm uterine fragments to induce endometriosis. The endometriomas were measured on days 1, 7, 14 and 21. The relative dry and wet weights of the endometrioma were used to evaluate response to the drug. Endometrial-like tissue was confirmed by histology. The greatest weight gain was observed on day 14 (relative wet weight: 29.1 ± 6.7 mg%, relative dry weight: 5.3 ± 0.9 mg %). Treatments were administered between day 5 and day 14. RESULTS The relative wet weight of the hemiuterus in the 10 mg/kg estradiol group differed significantly from control and the other two estradiol groups (p=0.0001). In the medroxyprogesterone acetate group the weight decreased significantly but this decrease was not dose-dependent. Weight reduction was also significant in the triptorelin pamoate and the acetylsalicylic acid groups. CONCLUSION The model of subcutaneous endometriosis is reproducible, low-cost and easy to perform, and suitable for the study of pathophysiology and the effects of drugs.