Recombinant human growth hormone (rhGH) promotes human T cell engraftment in mice with severe combined immunodeficiency, suggesting that rhGH may have effects on T cell adhesion and migration in vivo. The ability of rhGH to directly affect the adhesion capacity of human T cells to a variety of human or murine adhesion molecules and extracellular matrix proteins was examined. rhGH induced significant human T cell adherence to both human and murine substrates via either beta 1 or beta 2 integrin molecules. rhGH was capable of inducing significant migration of resting and activated human T cells and their subsets. Most of the migratory response to rhGH was chemokinetic rather than chemotactic. In vivo engraftment studies in severe combined immunodeficiency mice receiving human T cells revealed that treatment with rhGH resulted in improved thymic engraftment, whereas treatment with non-human-reactive ovine GH demonstrated no significant effects. These data demonstrate that rhGH directly augments human T cell trafficking to peripheral murine lymphoid tissues. rhGH appears to be capable of directly altering the adhesive and migratory capacity of human T cells to molecules of either murine or human origin. Therefore, GH may, under either isogeneic or xenogeneic conditions, play a role in normal lymphocyte recirculation.