The correlation between the increase of [Ca2+]i and the activation of hydrolysis of phosphoinositide-4,5-bisphosphate and formation of inositol(1,4,5)trisphosphate in neutrophils treated with Fc receptor-binding agonists is still under discussion. In this communication evidence is presented supporting the conclusion that, as it is widely accepted for the activation of other receptors, also upon the activation of Fc receptors the stimulation of the production of inositol(1,4,5) trisphosphate is involved in the increase in [Ca2+]i. In fact: i) treatment of neutrophils with immune complexes induced a very rapid phosphoinositide hydrolysis measured as [3H]inositol phosphates production from [3H]phosphoinositides and as inositol(1,4,5) trisphosphate formation measured with radioreceptor assay, ii) immune complexes caused a dose-dependent increase of [Ca2+]i; iii) the increase of [Ca2+]i correlated with the production of inositol(1,4,5) trisphosphate with respect to time course, dose dependence and pertussis toxin insensitivity.