A study was conducted using columns packed with Zorbax SIL, porous silica microspheres, with stationary/mobile phases formed from a ternary liquid system containing dichloromethane, methanol and water. Stationary phases were applied to the chromatographic support by the prolonged passage of mobile phase, saturated with stationary phase, through the pre-packed column. Although pronounced changes in retention characteristics were noted during the “in-situ” coating procedure, the overall selectivity remained reasonably constant. The resultant chromatographic system enabled a high degree of separation to be achieved between the closely related corticosteroids studied. A characteristic of the results was the very good peak symmetry, up to peaks with capacity factors, k′, of at least thirty. Examples given show the influence of the composition of the phase system on the retention characteristics of various corticosteroids.