The ability of human tonsillar lymphoid cells to express growth hormone receptor (hGH-N-R) was analyzed by flow cytometry. FITC-coupled recombinant human growth hormone (hGH-N) was used to reveal the receptors, in combination with phenotype markers.Unlike T cells, tonsillar B cells constitutively express the hGH-N receptor. Quiescent cells separated from activated cells by Percoll-gradient centrifugation bear fewer receptors than activated ones. Activated T cells express hGH-N-R, but the typical germinal centre CD4+CD57+ T cells do not. These latter thus appear not to be fully activated.Inside the lymph follicles, the germinal centre CD38+ B-cell population and the mantle-zone CD39+ B-cell population display similar levels of hGH-N-R expression, but receptor density is lower on dividing dark-zone CD38+CD10+ B cells.Different lymphoid-cell populations thus differ markedly in their ability to express the growth hormone receptor, in relation notably to their activation status. This highlights the link between the neuroendocrine system and the active immune defense.