T cells are known to be frequently numerous in follicular lymphomas but are generally considered to be a homogeneous population of small, round, "resting" lymphocytes. Although immunologic studies have suggested the presence of some "activated" T cells in these B-cell neoplasms, virtually no attention has been paid to the T-cell morphology. Wright-stained cytocentrifuged sheep erythrocyte (SRBC) rosette preparations from 20 cases of nodular follicular center cell lymphomas were therefore examined and the morphologic appearance of the SRBC rosetting cells was categorized. A mean of 19% (range 11-33%) of the SRBC-positive cells present were medium or large in size (diameter greater than two SRBCs, approximately 10 micron). A mean of 62% of SRBC-positive cells had round nuclei; 18% had indented nuclei and 20% had irregularly shaped nuclei. These data provide supportive morphologic evidence for some T-cell "activation" in certain follicular lymphomas. In addition to having possible functional and biologic implications, the previously undescribed presence of enlarged and sometimes "atypical" T cells in uncomplicated follicular lymphomas has implications for interpreting the histopathology of these B-cell neoplasms and the reported occurrence of composite T-cell/follicular center-cell lymphomas.