The effects of dietary medium-chain triglyceride (MCT) on the concentration of plasma ketone bodies in enterectomized and normal rats were examined, together with the effects on plasma glucose, plasma immuno-reactive insulin, and liver function. Four groups of enterectomized rats and four groups of normal rats were fed experimental diets containing 0, 6, 11, or 21% of MCT by weight for 6 days. All animals including normal rats received meal-feeding for 3 h once a day. On day 3, concentration of plasma ketone bodies in enterectomized rats increased dose-dependently with dietary MCT and the level was higher than that in normal rats. However, all the values in enterectomized rats never exceeded 2 mM, the maximum physiological concentration. In contrast, plasma glucose in the enterectomized rats showed a tendency to decrease more clearly and dose-dependently with dietary MCT, followed by a marked increase of insulin secretion compared with those in normal rats. On the final day, no significant differences in the results of liver function tests were observed among these groups. These results indicate that the MCT-induced ketosis was within an acceptable range, and dietary MCT is useful for the suppression of increase in plasma glucose following a surgical operation without any disadvantageous effects on liver function.