Using flow cytometry and fluorescence polarization analysis, specific muramyl peptide-binding sites were shown to be located inside T-lymphocytes, macrophages and neuroblastoma cells, but not inside B-cells. No binding sites were found on the cell surface. The number of binding sites for each cell type was determined. Two types of binding sites were observed for myelomonocytic WEH1-3 cells with Kfdvalues of 21 and 540 nM. Inhibition analysis demonstrated that for effective binding, an intact glycopeptide molecule and D-configuration of isoglutamine residue are important. © 1991.