In this investigation the cell cycle time and the life-span of cells in different tissues of the mouse eye were determined during postfetal development not with single but, instead, by means of repeated 3H-thymidine injections. The potential of this method applied for the first time in the mammalian eye, is thoroughly discussed. Essentially, four groups of 19-21 mice each, aged 1, 10, 20, and 60 days at the start of the experiment, received intraperitoneal injections of 3H-thymidine at a dose of 1 microCi/g body weight every 4 h for a maximum of 14 days, i.e. a total of up to 85 injections. Further animals were sacrificed after the 13th, 19th, 25th, 31st, 37th, 49th, 61st, 73rd, and 85th injections, i.e. 2, 3, 4, 5, 6, 8, 10, 12, and 14 days after the start of the experiment. When all the injections had been given, animals from each group were sacrificed on the 1st, 4th, 8th, 16th, and sometimes the 32rd, 48th, and 64th days, respectively, after the last injection. With this experimental paradigm it was possible: (1) to determine the cell cycle time and the life-span of the cells during postfetal development up to maturity without gaps; (2) to establish the end of the development by means of cell proliferation in various tissues of the mouse eye; herewith it was possible to determine the times at which the development by cell proliferation is replaced by development by cell differentiation, and (3) to clearly prove in which mature ocular tissues cell turnover still exists and in which it does not; this appears to be especially important, since in recent years the importance of cell proliferation process following injury and stimulation was also recognized in the eye, for example, in massive periretinal proliferation in connection with retinal detachment and retinal surgery, as well as in endothelial injuries following intraocular lens implantation; only when normal conditions are known can pathological proliferative processes be recognized as such and be distinguished from normal ones. The results are cumulatively represented in tabular form, from which details are to be extracted. As expected, cell cycle times are very short and seemingly homogeneous in tissues which develop within themselves, but become longer and inhomogeneous, except in the inner and outer granular layer of the retina, in which the cell proliferation comes to a particularly abrupt end. The shortest cell cycle time occurred in the cells of the vascular walls of the retina at the time of birth and was 24 h.(ABSTRACT TRUNCATED AT 400 WORDS)