Human peripheral blood polymorphonuclear leukocytes (PMNs) have recently been recognized as a heterogeneous population of cells. Consideration has not been given to the possibility that size may be an additional physical characteristic demonstrating heterogeneity. Using counterflow centrifugal elutriation, we have demonstrated that PMNs can be isolated into at least six volume-dependent fractions. A positive correlation exists for PMN size and superoxide anion release upon stimulation with f-Met-Leu-Phe or phorbol myristate acetate. Total granule contents were also noted to be greater in larger PMN fractions, with a constant percent of release upon stimulation. The implications of these findings are discussed.