An experimental technique to study the turnover of hyaluronan in the anterior chamber in single animals has been developed. It is based on the fact that circulating hyaluronan labelled with tritium in the acetyl group is rapidly taken up by the liver and degraded to tritiated water. 3H-labelled hyaluronan was mixed with high concentration, high molecular weight hyaluronan (Healon) and injected into the anterior chamber of rabbits. The concentration of tritiated water in blood plasma was followed for up to 13 days. An initial rise of radioactivity in the blood was followed by an exponential decrease. From the exponential disappearance it was possible to calculate the rate of turnover of water in the body. This was used to correct the initial rise of tritium for water losses. After this correction the appearance of radioactive water in blood corresponded to the disappearance of hyaluronan from the eye plus a 45 min time-lag due to the catabolism in the liver. Using this technique it was found that trace amounts of radioactive hyaluronan and 0.055 ml and 0.2 ml of 1% hyaluronan exhibited half-lives in the anterior chamber of 1.5, 7 and 13 hr respectively. When the same technique was used for subcutaneously and intramuscularly injected hyaluronan half-lives of 50 and 30 hr, respectively, were recorded.