1. Constant intravenous (3 h) infusions of a fructose solution were given on a rate for body-weight basis (0·6 g/kg per h) to thirty patients who had no evidence of diabetes mellitus or liver disease. Concentrations of blood fructose, pyruvate and lactate formed a plateau during the last 1–1·5 h of the infusion period.
2. Although the numbers were small, the individual pyruvate and lactate concentrations at plateau varied greatly and assumed a bi-modal distribution, suggesting two distinct groups. The group to show a lower pyruvate and lactate rise (group A) contained more males of a lower age and more patients who had ischaemic cardiac disease than the other group (B); none of these differences was, however, statistically significant. The fructose concentrations at plateau were not significantly different between the groups. Serum triglyceride glycerol concentration during the infusions rose markedly in three patients in group A but in none in group B. Minor changes in concentration of blood glucose, insulin, inorganic phosphate and uric acid during the infusions were not significantly different between the groups and did not fall into a bi-modal pattern.
3. Constant intravenous (3 h) infusions of 0.15M-sodiurn lactate at the same infusion rate in eight of the patients (four from group A and four from group B) did not produce a significant difference in the blood lactate concentrations at plateau between patients from the two groups.
4. These results reflect qualitative differences in fructose metabolism in the patients studied. The difference in pyruvate and lactate production may be associated with total carbohydrate intake. However, the bi-modal distribution strongly suggests a genetically determined difference in metabolism between the two groups.