To elucidate the mechanism of differentiating activity on L-Glu to HL- 60 cells, its influence on binding of human recombinant interleukine-1 β (rHuIL-1β), tumour necrosis factor-α (rHuTNF-α) and interleukine-6 (IL-6) by HL-60 cells was studied. It was established, that L-Glu converted the high affinity binding of [125I]rHuIL-1β (K(d) = 0.32 nM) and [125I]rHuIL-6 (K(d) = 0.075 nM) to HL-60 cells into low affinity (corresponding K(d) values - 13.3 and 2.1 nM) at concentration 0.1 μM. The preincubation for an hour of HL-60 cells with 0.1 μM L-Glu was shown to result in an increase of affinity and number of [125I]rHuTNF-α binding sites. Thus, L-Glu decreases the sensitivity of the HL-60 cells to IL-1β and IL-6 and increases TNF-α binding at concentration 0.1 μM.