Platelet-free cellular elements and non-hemolyzed, chemically unaltered serum are important research components of the cellular immunology laboratory. Both can be recovered from the same peripheral blood sample if it is properly defibrinated. The numbers of cells recovered from heparinized aliquots of blood from healthy donors were not significantly different from the numbers of mononuclear leukocytes, polymorphonuclear leukocytes, and erythrocytes recovered from blood samples which had been mechanically defibrinated in vitro with a stationary, cone-shaped 'TP'-like device which we here describe. Compared with serums obtained from clotted blood, or from blood defibrinated by using glass beads, we found that serums from blood defibrinated with the 'TP'-like device had the lowest detectable levels of hemoglobin, free DNA, or LDH. Serums from TP-defibrinated blood were not different from clotted serum samples with regard to the function of the classical complement pathway, the alternative complement pathway, C4 hemolytic activity, and most serum chemistries. Use of the TP-defibrinator in immunology laboratories is an ideal way to prepare blood for rapid isolation of cellular elements and non-hemolyzed serum from the same sample.