Sodium hyaluronates with molecular weights of 18000, 500000 and 4 x 10(6), labelled with either 3H or 14C, were injected into the anterior chamber or into the centre of the vitreous body of rabbits and their rates of disappearance were followed. The out-flow from the anterior chamber in anaesthetized animals was virtually independent of the molecular weight indicating that the disappearance of the polysaccharide is controlled by bulk flow. The rate constant for the disappearance of sodium hyaluronate was 0.0094/min and after treatment with indomethacin 0.0061/min. These figures are in general agreement with published flow-rates of aqueous humour in the rabbit. The disappearance from the vitreous body was strongly molecular weight dependent indicating a diffusion controlled transport. The rate constant for hyaluronate with mean molecular weight of 18000 was 0.16/day and 500000, 0.024/day. The rate constant for endogenous hyaluronate was estimated to be about 0.01/day. A calculation using these rate constants shows that the turnover of sodium hyaluronate in the rabbit anterior chamber is about 3 micrograms per 24 hr while the turnover in the vitreous body is only 15% of that. This confirms an earlier conclusion (Laurent and Granath, 1983) that the preponderant part of the hyaluronate in aqueous humour is not a general degradation product from the vitreous body.