A colony of NZW rabbits was developed in which 18 of 126 members exhibited overt symptoms of diabetes mellitus. On the basis of total body weight measurements, obesity does not appear to play a primary role in the development or manifestation of the syndrome. The relatively high frequency of occurrence of spontaneous diabetes mellitus in this colony seems to suggest a unique genetic predisposition of these rabbits, yet analysis of glucose tolerance of colony animals indicates no clear genetic mode of transmittance of the trait. Rather, data suggest a possible interaction of as yet undefined genetic and/or environmental influences as being responsible for the disease state. Regressions of k-value on age indicate an early predetermination of glucose intolerance in the rabbits. In addition to a planned program of breeding, investigations of dietary intake and possible relationships of the diabetic condition to bacterial or viral infections appear to be initial areas indicative of further study.