Lymphocyte subpopulations from 9 children with different rheumatic diseases were studied before and 5, 24 and 48 h after high dose intravenous methylprednisolone. Leu-1 (+) cells, Leu-2a (+) cells, Leu-3a (+) cells and surface immunoglobulin (+) cells were counted. A panlymphopenia occurred 5 h after infusion, but numbers of all cell types were normal by 48 h. B cells were less affected than T cells. Leu-3a (+) cells were relatively more decreased than the other populations at 5 h and took longer to return to prepulse levels. This suggests a selective difference in distribution of lymphocyte subpopulations after pulse methylprednisolone infusion.