In Reply.— The COMMENTARY Who Should Be Doing Gastrointestinal Endoscopy? was intended to address the problem of untrained persons attempting fiberoptic endoscopy on patients when expertise is available. The value of flexible sigmoidoscopy as a screening tool for colon cancer is not disputed. However, this half-a-loaf procedure (flexible fiberoptic sigmoidoscopy) 1,2 may lead to inadequate examinations when the need for total colonoscopy exists. Drs Felmar and Rodney agree that teaching the procedure is appropriate. The basic question concerns who should do flexible sigmoidoscopy. It should not be assumed that proficiency at rigid sigmoidoscopy implies competency to perform flexible sigmoidoscopy. It is not appropriate, therefore, to attempt flexible sigmoidoscopy without first obtaining training and demonstrating competency in the performance of the procedure. The training required to perform short colonoscopy with the 60-cm instrument may be less than that required for total colonoscopy, though the negotiation of the sigmoid-descending colon junction is