Abstract
(1) A tail-skin grafting method was used to test for histocompatibility differences between members of thirteen sublines of C3H inbred mice, kept in a 1 r./night gamma radiation field for twelve generations, on the average, and separated from each other by about thirty-four generations.(2) No homograft rejections occurred, so there was no evidence to suggest that mutations at histocompatibility loci had taken place in any of these sublines. Calculations show that this finding does not conflict with the idea that a fairly large number of loci are involved, having mutation rates similar to those already known in the mouse.