Dose-dependent inhibition of FMLP-induced neutrophil migration by various dilutions of RBC supernatant. Neutrophils were incubated in the upper compartment of a chemotaxis chamber in the absence or presence of various dilutions of RBC supernatant, and their locomotory response to 10 nM FMLP in the lower compartment was tested after 45 minutes' incubation. Results are expressed as mean ± 1 SD of 3 experiments with neutrophils from different donors.