This paper reports a difference in the lymphoid tissue area in the axilla of node-negative breast cancer patients in the first versus the second half of the year, the area being greater in the latter. This observations is new. It is based on data from 72 patients derived over 25 consecutive months and is in keeping with previous reports of a proliferative histological picture in the nodes at this time. The findings were less marked in the node-positive cases (23), and were not accompanied by an increase in nodal number. No such difference was seen in 80 specimens from noncancer autopsy controls. A total of 1,868 nodes were evaluated. The possibility that light-mediated reactions may be involved is discussed briefly, as is the role of this proliferative reaction and its probable mediation relative to the parallel histological changes reported in primary breast carcinomas at this time.