Dissolution rates in water of six oral 8-methoxypsoralen formulations were determined with both the rotating basket method and a column type flow-through method. Comparable and reproducible results were obtained with both methods. In view of the necessity in psoralen-UVA (PUVA) therapy that effective tissue concentrations of the drug be present in the skin during the irradiation period, we propose a requirement for a dissolution rate of 8-MOP tablets or capsules of at least 80% within 25 min. None of the three preparations registered in The Netherlands met this requirement. However, two preparations from abroad and a new capsule formulated in our pharmacy department with solid 8-MOP dispersed in polyethylene glycol 6000 showed satisfactory dissolution profiles.