The goal of the study was to evaluate the process of neutrophil activation via Ca(2+)-mediated transduction signal and its modification by insulin. The study was performed with the use of isolated peripheral blood neutrophils obtained from 20 healthy volunteers. Isolated granulocytes were stimulated by fMLP or insulin alone, or by both substances added to the medium in combinations: fMLP + insulin (after 20 min) or insulin + fMLP (after 20 min). To explore the mechanism of intracellular Ca(2+) changes, receptor signal transduction pathway was blocked by tyrosine kinase inhibitors: tyrphostin 25 and genistein. fMLP evoked fast intracellular increase of free Ca(2+) concentration in neutrophils, compared with the resting state (P< 0.001). Insulin did not cause any changes in intracellular Ca(2+) when was added to the previously fMLP stimulated cells. Prestimulation with insulin significantly decreased fMLP-induced intracellular free Ca(2+) concentration compared with fMLP alone (P<0.01). A strong correlation was observed between initial intracellular Ca(2+) concentration after incubation with insulin and the response to fMLP (P<0.0001). The tyrphostin 25 did not influence the Ca(2+) concentration in control granulocytes, but inhibited the fMLP-induced intracellular Ca(2+) increase when added before fMLP (P<0.05). In a Ca(2+)-free medium, a strong relationship between intracellular Ca(2+) and the response to fMLP after incubation with tyrphostin was found (P<0.001) The genistein did not influence the intracellular Ca(2+) in non-stimulated cells. However, it inhibited the fMLP-induced Ca(2+) increase when added before fMLP (P<0.05). The genistein added to the suspension of cells after fMLP stimulation did not influence intracellular Ca(2+) level. A positive correlation was found between the initial intracellular Ca(2+) and the response to fMLP of genistein preincubated cells. This effect was seen in both Ca(2+)-rich, and Ca(2+)-free medium We conclude that insulin is a potent immunomodulator and its signaling pathways are mediated by Ca(2+) concentration changes. The process of intracellular Ca(2+) changes following insulin signaling is, at least partly, tyrosine kinase-related. Derangements in the concentration of intracellular Ca(2+) may represent a link between the mechanisms of insulin resistance in diabetes.