Abstract: Water-insoluble pharmaceutically active substances such as cyclosporin are formulated for administration in the form of an oil-in-water microemulsion, wherein the active substance is fully dissolved in the dispersed oil particles. The oil is C.sub.8 to C.sub.20 fatty acid vegetable oil glycerides, and lecithin and another surfactant are included to form and stabilize the microemulsion in which the hydrophilic phase comprises propylene glycol. A preconcentrate comprising the above components but free from any hydrophilic phase can be utilized to make up the compositions, which are most suitably soft gelatine capsules or oral administration fluids. The glycerides are preferably from castor oil, coconut oil or peanut oil.