Thyroid hormones increase energy expenditure and bone turnover in vivo. To study whether 3,3',5-triiodo-l-thyronine (T(3)) stimulates the uptake of glucose in osteoblastic cells, PyMS (a cell line derived from rat bone) cells were kept in serum-free culture medium and treated with T(3). We measured [1-(14)C]-2-deoxy-D: -glucose (2DG) uptake and looked for expression of the high-affinity glucose transporters GLUT1 and GLUT3 by northern and western analysis. T(3) did not influence the cell number but slightly (1.3-fold) increased the protein content of the cell cultures. 2DG uptake was low in serum-deprived cell cultures and was increased by T(3) (up to 2.5-fold at 1 nmol l(-1) after 4 days) in a dose- and time-dependent manner. Triiodothyronine at 1 nmol l(-1) increased GLUT1 and GLUT3 abundance in membranes. Therefore, increased glucose uptake induced by T(3) in osteoblasts may be mediated by the known high-affinity glucose transporters GLUT1 and GLUT3.