The characteristics of cholesterol uptake by 83 human gall bladders (obtained at cholecystectomy) were studied with a modified Ussing technique. Real and artificial biles labelled with 14C-cholesterol and 3H-dextran (the latter to correct for adherent mucosal bile) were used; all gall bladders absorbed cholesterol (average 3.5 nmol/cm2/minute). Recovery of the absorbed cholesterol from the tissue showed that about 4% was esterified over 60 minutes. In artificial bile the rate of absorption of cholesterol increased as the bile saturation index rose, but became constant once supersaturation was achieved. In contrast, supersaturated real bile permitted greater absorption of cholesterol, possibly due to enhanced cholesterol solubilisation. Preincubation of gall bladder tissue in sodium cyanide (5 mM) caused a 30% reduction in cholesterol uptake indicating that, although absorption is predominantly a "passive" process, there is a partial "active" component. There were no pronounced differences in the rate of cholesterol absorption as gall bladders became more diseased, but there was a reduction in the amount of cholesterol ester formed.