Phagocytic activity and intracellular killing of opsonized staphylococci (Smith strain) by bovine blood polymorphonuclear leukocytes (PMNL) was studied after their migration in vitro in blind well chambers. The results indicate that migration of PMNL to RPMI-1640 medium without chemotactic factor significantly (P less than 0.01) increased the percentage of rosette-forming PMNL (from 11 +/- 2 to 49 +/- 4%), as well as phagocytic activity mediated through Fc receptors (FcRs) (from 25 +/- 3 to 81 +/- 4% phagocytizing PMNL and from 151 +/- 22 to 942 +/- 54 number of phagocytized staphylococci/100 PMNL), and intracellular killing of bacteria (from 13 +/- 2 to 59 +/- 7%). On the other hand, PMNL migration to RPMI-1640 medium with the chemotactic factor (serum activated with zymosan [AS] or lipopolysaccharide [LPS] or formyl-L-methionyl-L-leucyl-L-phenylalanine [fMLP]) did not significantly (p greater than 0.05) increase either the FcRs number on the PMNL surface or the phagocytic and bactericidal activity connected with these receptors. The possible mechanisms are discussed.