Abstract We examined morphometric as well as functional characteristics of CD16-positive human peripheral blood lymphocytes on the basis of the coexpression of the CD2 antigen. For morphometric analyses, nuclear area and cellular area were determined by counting line cross-points of a superimposed quadratic lattice test system overlying nuclei and the whole cell, respectively. Moreover, to evaluate the cellular villousity degree, the maximum inscrible circle and an irregular polygon were inscribed within cell profiles. The cytoplasm fraction included between the plasmalemma and the traced irregular polygon was considered as the villous portion of the cell. Finally, the NK capability was measured in a 6-hr 51Cr-release assay with human K-562 myeloid cells as targets. Within the CD 16-positive cell population, the CD 16-positive/CD2-negative cells seem to represent the most efficient NK cell subset. To the higher NK capability correspond a higher villousity degree and a lower nuclear area/cellular area ratio of the CD2-negative/CD16-positive subset, when compared with CD2-positive/CD16-positive cells.