IL-15 administration does not affect thymocyte distribution in recipients of an allo TCD-BMT at day 28. Lethally irradiated (1300 cGy) CBA/J recipients received transplants of B10.BR TCD-BM (5 × 10⁶) and 2.5 μg/d IL-15 or PBS (control) on days 21 through 27 by intraperitoneal injection. BMT recipients were killed at day 28, and percentage and absolute numbers of donor-derived cell populations in the thymi were calculated from total cell counts and multicolor flow cytometric analyses of thymocyte cells with anti-CD4 and anti-CD8. Donor or host origin was determined with anti-Ly 9.1, which is present on host leukocytes. Values represent the median cell numbers (n = 10) ± a percentile range (25% and 75%).