We show that the LFA-1 molecule on T cells does not play a role in the stimulation of T cell hybridomas by certain targets, namely antigen presented by L cell derivatives or polyvalent anti-receptor antibody. These results suggest that LFA-1 may act by binding to ligands that are not present on all cells. We hope this result will help us and others to establish the true role of LFA-1 in T cell responses.