A method has been developed which allows the kinetics of oral mucosal drug absorption from solutions to be studied in a single 15-20 min test. This is an improvement over the traditional buccal absorption test which requires a separate experiment for each time point, thus taking days for each kinetic profile. It should also allow for disappearance of drug from the mouth and appearance in the plasma to be monitored simultaneously. The drug solution includes 8 micrograms mL-1 phenol red as a marker for salivary secretion. Samples are withdrawn at suitable times with a positive displacement pipettor and analysed for drug and phenol red. Salivary volume time data are described by least squares polynominals. Kinetic parameters are estimated by non-linear least squares regression. The method, which requires that phenol red is not lost during a test, provides an internal test for this. It also requires that phenol red and the drug do not interfere with each other's assay, that saliva does not affect the assays of these materials, and that phenol red does not interfere with the absorption of the drug.