Peritoneal contamination with bacteria during the laparoscopy and dye procedure was studied in 38 subfertile women by culturing samples of peritoneal fluid, aspirated before, and after, injection of dye solution. Bacteria were carried with the dye into a previously sterile peritoneal cavity in 34 women (90%). These vaginal organisms were present in low concentrations, not exceeding 10(5) organisms/ml. These findings explain the low incidence of acute salpingitis after tubal patency tests, but the selective use of antibiotic prophylaxis is recommended.