IL-7 moderately affects thymopoiesis. IL-7 administration resulted in a moderate but not significant increase in the frequency of TREC copies per 10⁵ donor-derived CD45.1⁺ thymocytes at day 28. Recipients of T-cell–depleted BMT treated with IL-7 (n = 9) or PBS (n = 9) were killed at day 28 and thymuses were evaluated for numbers of TREC copies per 10⁵ bone marrow–derived CD45.1⁺ thymocytes. Horizontal bars indicate medians.