Interleukin (IL)-1beta may effectively decrease introcular pressure (IOP) when administered by subconjunctival injection in normal rabbit. However, IL-1beta is a large molecular agent and an inflammation factor. The aim of this study was to evaluate the penetrability of IL-1beta, and the concentrations of both tumor necrosis factor (TNF)-alpha and IL-6 in the aqueous humor of normal rabbits treated with IL-1beta.A total of 170 rabbits were used in the study and were assigned to several different treatment groups as follows: 125 of the rabbits were assigned to two groups. In one group, 33 rabbits were injected subconjunctivally with IL-1beta and 39 were injected with saline alone. In the other group, 27 rabbits were given eye drops containing IL-1beta (400 ng/ml) and 26 were given saline alone. Aqueous humor (AH) was drawn and the concentration of IL-1beta within the fluid measured. The IOP was measured in another six rabbits after administration of eye drops containing IL-1beta (400 ng/ml). A further 20 rabbits were assigned to 3 groups as follows: eight untreated normal controls; six injected subconjunctivally with IL-1beta; and six injected subconjunctivally with saline alone. AH was drawn and the concentration of TNF-alpha in the fluid was measured. Another 19 rabbits were assigned to 3 groups as follows: seven untreated normal controls; and six injected subconjunctivally with IL-1beta; and six injected subconjunctivally with saline alone. AH was drawn and the concentration of IL-6 in the fluid measured. Measurement of cytokine concentration was by radio-immunoassay in all cases.The IL-1beta concentration in the AH was higher in those animals in which it had been administered subconjunctivally (P < 0.01). The IL-1beta concentration in the AH of the animals given eye drops was almost the same as that in the controls (P > 0.05). The administration of IL-1beta in the form of eye drops had little effect upon IOP reduction. Lower TNF-alpha concentrations were seen in the AH after the subconjunctival administration of IL-1beta, but the concentration of IL-6 was the same as in the normal controls.IL-1beta shows good corneal penetrability after subconjunctival injection into normal rabbit eyes. The IOP reduction induced by IL-1beta is unlikely be associated with an inflammatory response.