Human lymphoid cells were examined by scanning electron microscopy (SEM) to see if a correlation existed between surface morphologic features and the presence of various surface markers and receptors. When viewed by SEM thymocytes appeared as smooth-surfaced cells with few surface microvilli; peripheral blood lymphocytes (PBL) on the other hand were moderately to densely villate with no entirely smooth-surfaced cells observed. Surface morphology within PBL samples was not uniform, due mainly to variations in the shape and number of microvilli. However, 2 distinctive types of surface morphology (termed Types 1 and 2) were discernable with a small number of cells displaying features of both groups (Type 3). The majority of E-rosette forming cells (T lymphocytes) displayed Type 1 and the majority of cells bearing demonstrable surface immunoglobulin (B lymphocytes) displayed Type 2 morphology. Exposure of PBL to anti-T cell specific ALG resulted in cytolysis of cells with Type 1 morphology while cells with Type 2 morphology appeared largely unaffected. PBL with Fc and C3 receptors displayed all 3 types of morphology. It is concluded that T and B lymphocytes do have subtle but nevertheless discernable differences in surface morphology and within these 2 groups, variations in surface morphology are probably associated with changes in the physiological status of the cell.