In order to induce steroid cataracts in rat lenses, prednisolone acetate was administered together with a single subliminal dose of X-irradiation, which was applied unilaterally before steroid application started. The rats were divided into a control group (without prednisolone acetate administration), a group with a topically administered daily dose of 1 mg/kg prednisolone acetate suspension and a group with a systemically applied daily dose of 0.8-1.0 mg/kg prednisolone acetate suspension. Changes in the lens were objectively evaluated with in vivo Scheimpflug slit images during a 30-week period. Although body weight increase was significantly affected in both groups administered prednisolone, animals survived until the end of the observation period. The initial changes in the lens were the dissociation of the Y-suture and a slight increase in scattering light intensity at the posterior embryonic nucleus after both topical and systemic steroid administration.