Repeated KGF treatment (3 monthly courses of 3 days each) maintained enhanced thymopoiesis in aged mice. The thymic cellularity was analyzed after a single course or multiple courses of KGF treatment to aged mice. Mean absolute thymocyte numbers ± SD from PBS-treated young mice (▥); aged mice evaluated 3 months after PBS treatment (⊡); aged mice 3 months after a single course of KGF treatment (□); or aged mice 3 months after initiation of monthly courses (3) of KGF treatment (▧) (n = 5 in each group). *P < .05; NS indicates not significant.