The interrelationships between the immune and neurohormonal system are the subject of this work. In this context, the formation of inositol-1,4,5-tris-phosphate (IP<sub>3</sub>) in response to cholinergic stimulation was studied in activated human peripheral blood mononuclear cells (PBMC) and lymphocytes from the lymphoblastoid cell lines Jurkat and Raji. The cells were stimulated with mitogen and then treated with either the cholinergic agonist carbachol or nicotine. The radioreceptor assay was used to determine IP3. Cholinergic agonists increased the level of IP<sub>3</sub>in all studied lymphocytes. Maximal level of IP<sub>3</sub>was observed in PBMC after stimulation with nicotine, whereas in Raji cells IP<sub>3</sub>level significantly increased after stimulation with carbachol and nicotine. These results indicate that the effect of stimulation of cholinergic receptors present on the activated human lymphocytes appears to be followed by an enhancement in the rate of polyphosphoinositide hydrolysis.