The number of cell surface FMLP receptors expressed by peripheral blood neutrophils taken from healthy individuals was quantitated using a direct fluorescence label analysed on the FACScan. Receptor numbers, assayed on cells from heparinised blood prepared at 4 degrees C or 37 degrees C or in the presence of LPS (30 ng/ml) were 12,540 +/- SD 2413, 18,588 +/- 4938 and 45,041 +/- 10,744 respectively. Anticoagulation with EGTA resulted in 25-30% greater basal receptor numbers but had no effect on receptor level after maximal stimulation with LPS. Double labelling with a neutrophil-specific mAb showed that the entire neutrophil population expressed FMLP receptors.