A new model, the dispersion model of hepatic elimination, is applied to the correlation between in-vitro microsomal data and corresponding rat isolated perfused liver data for a number of drugs reported in the literature, whose extraction ratio varies over the range of 0.01 to 0.995. The dispersion model described the data better than either the 'well-stirred' model or the 'parallel-tube' model, two other widely used models of hepatic elimination. The experimental data support the concept that elimination of solutes is affected by is a considerable dispersion on passage through the liver.