Intraocular injection of highly purified human interleukin 1 into the anterior chamber of the rabbit eye resulted in the accumulation of inflammatory cells. Peak cellular infiltration occurred at 4hr and cells were still present at 24h. Examination of ocular blood vessels in IL-1-injected eyes revealed no abnormalities. IL-1 had no effect on the protein content of the aqueous humour confirming that this monokine has no direct action on the blood-aqueous barrier. Comparison of the potency of IL-1 as a chemoattractant with the 5-lipoxygenase product, leukotriene B4 demonstrated that the former agent was more active by several orders of magnitude.