A study was carried out on the stability of dilutions of creams and ointments of two corticosteroids, betamethasone valerate and beclomethasone dipropionate. A reversed-phase high-performance liquid chromatographic method was developed that is simple, efficient and stability-indicating in respect of the main decomposition products and has the advantage of being carried out at ambient temperature. The effect of water content of the sample solutions and the influence of large injection volumes (200-250 mul) on the resolution of the substances on the chromatogram was investigated. Use of the diluents, cetomacrogol cream (formula A) BP and white soft paraffin BP, resulted in satisfactory products in terms of chemical stability and efficacy of antimicrobial preservation.