Thirty-one patients complaining of unexplained infertility for at least 36 months and diagnosed elsewhere were reassessed laparoscopically. After staining their pelvic peritoneum with concentrated methylene blue, they presented with extensive areas of dark blue discoloration, and were diagnosed as suffering from ‘diseased pelvic peritoneum’. The levels of peritoneal CA 125 were assessed. At the end of the diagnostic procedure, bipolar electrocoagulation or defocalized laser beam therapy was performed to destroy the affected peritoneal areas, and to allow peritoneal regeneration. Twenty-five pregnancies were obtained following this treatment. A detailed description is given of the diagnosis and treatment procedures.