The utilization of fructose and glucose by fibroblast cultures obtained from patients with hereditary fructose intolerance (HFI) was studied in comparison with fibroblast controls. The cell growth, the time course of D-glucose or D-fructose uptake and the consumption of fructose were similar for both HFI and control cells. Some results showed significant differences between these two cell types: HFI cells consumed less glucose, produced less lactate and contained less glycogen than control cells. Furthermore, significantly less [U-14C]D-glucose and [U-14C]D-fructose was incorporated into lipids in HFI cells than in control cells. The mechanisms responsible for these differences observed between the two cell types are not known.