Different Percoll density gradients were used to purify granulocytes from Long-Evans, Fischer, Sprague-Dawley, and Fischer/Long-Evans hybrid rats. Three different discontinuous gradient types were developed which permitted the separation of polymorphonuclear leukocytes (PMNLs) from the peripheral blood of the different rat strains. Our purification techniques were compared to each other in terms of purity and yield. Purities of 97.7 +/- 0.6%, 97.0 +/- 1.1%, 96.4 +/- 1.2% and 96.7 +/- 1.1% were achieved for the granulocyte fractions of LE, F344, SD and FL/F1 rats, respectively. The superoxide production of the isolated cells was also investigated and it was established that the granulocytes could be activated by phorbol-12-myristate-13-acetate (PMA).