The results of kinetic studies of AIB uptake into rat liver slices suggested that AIB is transported into this tissue by at least two distinct transport systems which may differ in respect of their Na dependence and their kinetic characteristics. Only the Na+‐requiring low‐Kt mode of uptake seems to show diurnal rhythm changes. Uptake velocities at low AIB concentrations in the incubation medium were analysed by Lineweaver‐Burk plots. The data revealed that the daily maximum of AIB transport is primarily due to a reduction of the apparent Ki for AIB uptake.