Exogenous IGF-1 enhances thymic output. Recombinant human IGF-1 was administered by continuous infusion using subcutaneously placed osmotic pumps to deliver a dose of 100 μg/day for a total of 2 weeks in 8- to 12-week-old thymus-intact female C57BL/6 mice. Pumps were replaced to deliver another 2-week course of continuous IGF-1 at 100 μg/day for a total course of 4 weeks. Combined spleen and lymph node data were obtained after 4 weeks of IGF-1 treatment: (A) CD4⁺ subsets; (B) CD8⁺ subsets; and (C) total TRECs from separated CD4⁺ and CD8⁺ T cells. Presented data are representative of 3 independent experiments, with 4 mice per group per experiment. *P < .05 between IGF-1– and diluent-treated mice. Error bars represent SEM.