The authors appreciate the thorough comments of Drs Barrett and Maresh concerning their observations of pelvic fluid in 20 consecutive laparoscopies.Although cul-de-sac fluid may be found routinely at laparoscopy and colposcopy, we have observed it only ultrasonically during the periovulatory period. As suggested by Drs Barrett and Maresh, this midcycle pelvic fluid may merely exceed the threshold necessary for ultrasonic detection. Assuming this threshold effect, ultrasonically estimated volumes will understandably be less than those directly measured in surgery.In our study, fluid was seen in eight of 20 midcycle examinations. The remaining cycles may not have exceeded the threshold amount necessary for ultrasonic visualization. Alternately, as we mentioned, the periovulatory threshold could have been missed by our sampling technique.A correlative ultrasound-laparoscopy study would, of course, be ideal to document accurately the fluctuation of pelvic fluid and its relationship to Mittelschmerz.