The effect of organophosphate pesticide--Chlorfenwinfos on the selected parameters of humoral and cellular immunologic response in mice was investigated. Hematologic and histologic examinations were run parallelly. The animals were treated with pesticide p.o. during 90 days in doses 1/100, 1/50 and 1/25 of LD50. It was found that Chlorfenwinfos exerts immunotropic effect. After high doses the strong suppressive effect in PFC and EA rosettes was observed. Significant involution of thymus was noted. Il-1 activity, DTH reaction (24 h after challenge) and endogenous and exogenous spleen colonies were stimulated. It seems that immunotropic effect of this pesticide is reversible. Three weeks after the exposure to this compound had been stopped, PFC, IgG and IgM level came back to the normal value.