Previous studies have demonstrated that lymph node cells of mice skin-sensitized 24 h before are able to transfer contact sensitivity (CS) in naive recipients. These antigen presenting cells (APC) lose the ability to induce CS when donor mice are treated with the virus of Newcastle Disease (NDV) at the time of sensitization. In this paper we demonstrate that the cell capable of suppressing CS is a virus induced plastic adherent T-cell, which inhibits otherwise normal APC. In fact, the APC in infected mice are fully competent, as demonstrated by their ability to transfer CS, if the adherent T-cell population is removed by plastic adherence. Analysis shows that the CS suppressing adherent T-cells are Thy 1.2+, Lyt 1.1+ and I-J+ subset. The inhibition of CS by the NDV induced adherent T-cell is antigen non-specific and genetically restricted. We have also demonstrated that picrylated cells from NDV infected mice fail to trigger the release of non-specific inhibitor (nsINH) in the T-suppressor circuit. The effect of the adherent suppressor T-cell in that circuit was determined and the results indicate that the virus induced T-cell is able to suppress the release of nsINH by blocking the function of the APC.