The effect of daily oral administration of corticosteroids on ocular dynamics and biosynthesis of corneal mucopolysaccharides was investigated using rabbits as experimental animals. Fluocortolone treatment at doses of 0.05 to 10 mg/kg resulted in a dose-dependent rise of intraocular pressure (IOP). At higher dose levels of 5 and 10 mg fluocortolonel kg daily over 14 days, an inhibition of 35S-incorporation and a reduction in the nexosamine content of the corneal mucopolysaccharides was observed. When the effects of prednisolone, fluocortolone and dexamethasone on IOP were compared the relative order of the potency for the corticosteroids was as follows: dexamethasone > fluocortolone > prednisolone. The influence of different doses of fluocortolone on ascorbic and sialic acid content in aqueous humour and plasma was also studied. Levels of 5 and 10 mg/kg caused a significant reduction of ascorbic acid and a slight increase in sialic acid content in aqueous humor besides an elevation of IOP, whereas the plasma levels of both components did not reveal any difference from control group. These findings suggest that the blood-aqueous barrier becomes more permeable under the treatment with corticosteroids, especially in doses which are known to be toxic in animals. Further, the rabbit can be used as an experimental animal for comparing the effets of different corticosteroids on IOP.