The occurrence of nuclear pockets in leukocytes was studied in four groups of dairy cattle. These were animals with 1) normal hemograms from leukemia-free herds, 2) normal hemograms from multiple-case leukemia herds, 3) persistent lymphocytosis from multiple-case leukemia herds, and 4) clinical leukemia. These nuclear pockets generally resembled those in man and other species, but were limited to lymphocytes. Statistical evaluation of the frequency of occurrence of nuclear pockets in the lymphocytes of these four groups showed that: 1) Lymphocytic and leukemic animals had six times as many lymphocytes with nuclear pockets as animals with normal hemograms. Differences were significant both in mean frequency of lymphocytes with nuclear pockets (39.9 vs. 6.8/thousand) and in their distribution. 2) The difference in mean frequency of nuclear pockets in animals with normal hemograms from leukemia-free herds was not significant as compared to normal hemogram animals from multiple-case leukemia herds. However, the latter group had a significantly higher variance. 3) Lymphocytotic and leukemic animals belong to one common population in terms of mean frequency and variance of occurrence of lymphocytes with nuclear pockets.