With autoradiographic and cytophotometric methods, the labelling index and ploidy pattern of the cells of the lacrimal gland, the glandula orbitalis externa and the glandula infraorbitalis of male and female rats of different ages (1,3,6 and 12 months) were investigated. The nuclei of the lacrimal glands showed a predominantly diploid pattern in both sexes. Only the 12-month-old male and female rats showed a small number of tetraploid nuclei In contrast, beginning with 3 months, both male and female rats exhibited a large number of tetraploid nuclei in the glandula orbitalis externa and glandula infraorbitalis. In addition, the female rats displayed round nuclei and the male rats exhibited dumb-bell-shaped nuclei. The dumbbell-shaped nuclei in the males were a result of what appeared to be polyploidisation. With the increase in polyploidisation, there was a simultaneous decrease in the DNA content and an increase in the labelling index. This indicated that these cells had a decreased turnover. The mechanism for the apparent polyploidisation of the male rats, beginning in the 3rd month, is discussed.