The potential of photodynamic therapy for endometriosis was evaluated by autotransplantation of endometrial tissue in 15 female virgin New Zealand white rabbits. After maturation, 14 animals were injected intravenously with 10 mg/kg of dihematoporphyrin ether (DHE) and, 24 hours later, transplants were exposed to 630 nm light at 100 to 210 mW/cm2. Sixteen transplants received 100 J/cm2, 10 transplants received 50 J/cm2; 13 untreated transplants served as controls. In the remaining animal that did not receive DHE, 3 transplants were irradiated with 100 J/cm2. Six days after treatment, transplants were harvested with the underlying musculature, and multiple sections were examined histopathologically. Complete endometrial epithelial destruction was seen in 13 of 16 transplants (81%) in the 100 J/cm2 group and in 6 of 10 transplants (60%) in the 50-J/cm2 group. Nearly complete endometrial epithelial destruction was seen in 2 other transplants in each group. No damage occurred in either the 3 transplants that received 100 J/cm2 without prior DHE or in the 13 transplants with DHE and no irradiation. The sensitivity of ectopic rabbit endometrial tissue encourages further evaluation of photodynamic therapy for the treatment of human endometrial disorders.