Previous studies have documented that the interaction of IgG immune complexes with the FcIgG receptor (Fc-IgGR) of human T lymphocytes induces alterations both in the expression of Fc receptors and in the functional capacities of these cells. After IgG immune complex exposure, Fc-IgGR-bearing T lymphocytes lose their Fc-IgGR and generate Fc-IgMR in subsequent culture. This transition phenomenon is mediated via patching and capping of the Fc-IgGR. Since Colchicine and Cytochalasin B have been demonstrated to interfere with capping of other membrane elements by their known effects on cytoskeletal structures, we investigated the effects of these agents on the expression of Fc receptors of human T cells. Neither Colchicine nor Cytochalasin B directly affects Fc-IgGR or Fc-IgMR expression. However, both agents inhibit the loss of Fc-IgGR subsequent to IgG immune complex exposure as well as the development of Fc-IgMR in culture. Immunofluorescent studies illustrate that this inhibition is mediated in part by interference with capping of the Fc-IgGR-immune complex ligand. This study emphasizes the inverse relationship between Fc-IgGR and Fc-IgMR expression on human T lymphocytes.