In the present study the inhibition by nedocromil sodium of the specific receptor binding of FMLP was evaluated in human neutrophils (PMNs) using a FMLP-(3H) binding assay. The time course of the binding was markedly influenced by nedocromil sodium used at a concentration of 300 microM. No significant inhibition was obtained when the cells were treated with nedocromil sodium 3 microM or with sodium cromoglycate 300 microM. FMLP binding is essentially eliminated by the highest dose of nedocromil sodium. The biologic meaning of this effect in asthmatic patients should be further evaluated.