The previous finding noted in man of significant difference in endogenous lipoprotein lipase (ELPL) activity of plasma in oral glucose tolerance test (OGTT) between diabetic state and non-diabetic state has been confirmed and attested by experiments in rabbits. Observations were also made of plasma lipid changes associated with OGTT and of those in rabbits with developing steroid-diabetes by corticosteroid injection, with the results as follows. 1) In OGTT, non-diabetic state exhibited a bi-peaked curve for plasma ELPL activity with maxima at 90 and 150 minutes after an oral dose of glucose whereas diabetic state showed an activity curve with a single peak at 90 minutes after oral glucose administration. 2) In OGTT, non-diabetic rabbits (maintained on bean-curd refuse diet or lanolin diet) exhibited a bi-peaked curve for plasma ELPL activity with maxima at 30 and 120 minutes after an oral dose of glucose whereas rabbits with alloxan-or steroid-diabetes showed an activity curve with a single peak at 90 minutes after oral glucose administration. 3) During the OGTT the animals displayed prominent changes in plasma nonesterified fatty acid levels while such other plasma lipid factors as triglycerides, total cholesterol, phospholipid and total lipid remained virtually unchanged. 4) Steroid-induced diabetes was faster in onset in lanolin fed rabbits with hyperlipidemia, compared with animals maintained on bean-curd refuse diet. 5) The most prominent feature of abnormal lipid metabolism observed in rabbits with developing steroid-diabetes was elevation of serum triglycerides. 6) Principal fatty acid levels in the plasma of rabbits receiving a corticosteroid were determined at certain time-intervals during the OGTT. All these fatty acids showed changes with time, being particularly marked at 180 minutes after glucose administration; changes of palmitic acid, oleic acid and linoleic acid concentrations were conspicuous in both the bean-curd refuse fed group and the lanolin fed group.