A preliminary survey has been completed using manual densitometric technics to determine the mean retinal circulation times in groups of normal controls, offspring to two diabetic parents with normal glucose tolerance (prediabetics), and offspring of two diabetic parents with abnormal glucose tolerance (chemical diabetics). Comparisons of the mean retinal circulation time showed differences between the left eye and right eye in prediabetic and chemical diabetic groups and a sex difference in both normals and prediabetics. In addition, both age and per cent ideal body weight were inversely related to the mean retinal circulation time. The levels of fasting serum cholesterol, triglyceride, and growth hormone, in many instances, also appeared to be inversely related to the mean retinal circulation time. Similarly, the degree of glucose tolerance (determined by the area under the glucose curve above baseline) was significantly inversely related to the mean retinal circulation time. The mean retinal circulation time adjusted for per cent ideal weight was analyzed separately for both right eye and left eye, and a significantly shorter mean retinal circulation time was noted, particularly in males, for prediabetics than for normal controls and for chemical diabetics than for both prediabetics and normals. Analysis of the mean retinal circulation time adjusted for age showed similar differences. It is postulated that the genetic prediabetic state with or without glucose intolerance might be associated with significant alterations of mean retinal circulation time independent of age and per cent ideal weight. It is also suggested that a number of potentially meaningful interrelationships between the degree of glucose intolerance and/or hyperlipidemia might exist and should be further quantified.