The absorption of a range of steroids (water soluble to lipid soluble) in the mouth was investigated under standard conditions and using gas chromatography. A two-compartment open model was used to describe the absorption of these steroids into, and through, the membrane. Rate constants were calculated on this basis using a feathering technique, and were used in an analogue computer program to predict steroid concentration which agree favourably with experimental data. Correlations between absorption and partition data were made in an attempt to relate the proposed model to anatomical features of the absorptive membrane and to make comparison with models proposed to describe drug absorption across the intestinal mucosa.