Adult mice were sensitized with bovine gamma globulin and complete Freund's adjuvant. Each mouse had received tritiated thymidine every 3 days before killing, and autoradiographs were prepared. In the sensitized group, proliferaion of lymphocytes and percentage of labelled cells was markedly increased in the draining lymph nodes espescially 5-7 days later.
Proliferation of labelled small lymphocytes were also noted.