The uptake of 59Fe ascorbate by suspensions of human enterocytes prepared from endoscopically derived duodenal biopsies was studied, with each subject's serum ferritin concentration determined at the time of endoscopy. Iron uptake was greatest at 37 degrees C. Uptake increased from pH 5.5 to 7.3, before being totally inhibited at pH 9.0. However, ferrous ion concentration, determined by 3-(2-Pyridyl)-5,6-bis(4-phenyl sulfonic acid)-1,2,4-triazine, was greatest at pH 5.5 and fell over this pH range. The rate of uptake was significantly greater by enterocytes isolated from individuals with a low serum ferritin (< 22 ng/L) compared with those with normal serum ferritin (> 22 ng/L). Vmax +/- (SEM) was 78.7 +/- 8.5 pmol Fe/(micrograms DNA.min) in the normal group (n = 12) and 141 +/- 17.2 pmol Fe/(micrograms DNA.min) in the low ferritin group (n = 4, P < 0.008). Corresponding Km values were 52.5 +/- 11.7 and 66.7 +/- 5.1 mumol/L, respectively (P < 0.91). Zinc, lead, cobalt and manganese added to the incubation buffer significantly lowered iron uptake into cells (unselected patients). The concentrations of each metal required to halve the uptake rate from 50 mumol/L iron (IC50) were 85 +/- 5 mumol/L (Zn), 570 +/- 170 mumol/L (Pb), 1.1 +/- 0.1 mmol/L (Co), and 3.8 +/- 0.7 mmol/L (Mn). The results demonstrate that enterocytes isolated by this method show the characteristics of iron uptake seen in animal studies. We suggest that these cells will be useful in the study of iron uptake in humans.