This study explored the intracellular signals that control the acquisition and maintenance of locomotory capacity in T lymphocyte line Jurkat. The majority of the actively dividing Jurkat cells show an immotile morphology. It was possible to induce the polarization and locomotion in the majority of these cells by culture in the presence of dibutyryl cyclic AMP for at least 3 days. Such culture resulted in a decrease in the Jurkat cell size, in a block in the first gap phase of the cell cycle and in an increased surface expression of CD3. These cells displayed a constitutively motile behaviour which was temperature and energy dependent. The polarization of the Jurkat cells was permanently reversed, in a short-term assay, by PH A and drugs which increase the phosphorylation of intracellular proteins (phorbol esters and phosphatase inhibitors) and which increase intracellular concentrations of cAMP. In contrast, the polarization was reversed transiently following a stimulation of the T cell receptor complex by an CD3 monoclonal antibody or when the intracellular Ca2+ stores were emptied as a result of the inhibition of Ca2+ pump by thapsigargin. The effect involving PH A, CD3 and thapsigargin is dependent on the presence of extracellular Ca2+. The evidence suggests that PKC is the most important and common element in the inhibition of the polarization process in Jurkat cells. Indeed, the activity of most agents could be partially and dose-dependently inhibited using PKC inhibitors. The signal, which leads to the inhibition of polarization in dbcAMP- cultured Jurkat cells is coupled by a tyrosine kinase as well as by a pertussis toxin-sensitive G protein