Earlier work shows that hyperlipemic type II diabetics tolerate wide ranges of sucrose and carbohydrate intake without effects on glycemic control, but a rise of fasting serum triglycerides sometimes occurs. To address further the issue of individual susceptibility to carbohydrate, the current study was designed to use each patient as his own control when given diets widely varying in sucrose content. After a stabilization period in the hospital on a normal sucrose content diet, each subject was given either a very low sucrose (less than 3 gm/day)-low carbohydrate (38 +/- 2%) diet or a high sucrose (220 gm)-high carbohydrate (63 +/- 3%) diet for 4 weeks. On a separate admission the opposite diet was assessed, again after an initial normal sucrose content diet. No consistent differences occurred in serum glucose levels or in 24-hr urinary glycosuria. High sucrose-carbohydrate intake raised fasting hypertriglyceridemia after 2 weeks but less thereafter. Severe sucrose-carbohydrate restriction did not significantly decrease fasting serum triglycerides; postprandial triglycerides changed in a trend opposite to fasting levels. No differences occurred in fasting serum insulin or serum cholesterol levels, but postprandial insulin levels were higher in high sucrose-carbohydrate diets. A diet with low sucrose and low total carbohydrate appears to offer no improvement in glycemic control over at least 70-fold higher dietary sucrose levels. However, high sucrose and carbohydrate diets increase fasting triglyceride levels in hypertriglyceridemic type II diabetics.