The length of distal margin between the lower border of the tumour and the level of division during low anterior resection may be related to the rate of local recurrence. The method of measuring the distal clearance is not usually stated in reports of the operation. The distal margin was measured prospectively in 5 different ways in 20 patients. A difference was observed between various methods of measurement of the same specimen in situ, unpinned and pinned out before and after fixation. The margin was significantly less (p less than 0.001) in unpinned compared with pinned specimens. There was poor correlation between the in situ measurement and that determined by the pathologist in both unpinned and pinned specimens. There was no significant difference before and after fixation if the specimen had been pinned but significant (p less than 0.001) shrinkage occurred with fixation when the specimen had not been pinned.