AbstractSeptilin is a polyherbal preparation, claimed to be effective in conditions such as chronic stubborn URTI, tonsillitis, cutaneous infections, dental infections and also prescribed as a health supplement. In view of this, the present experimental study was undertaken to evaluate the effect of Septilin on different arms of the immune system. The experimental animals (male albino rats and mice) were divided into three groups. Group I received distilled water; group II received Septilin in a dose of 1 g/kg (rats) or 1.5 g/kg (mice); group III received Septilin 2 g/kg (rats) or 3 g/kg (mice) orally for 28 days. They were evaluated for immunological function on day 29 by studying weight gain, resistance against E. coli sepsis, haemogram, phagocytic activity of PMN cells and reticuloendothelial system, delayed hypersensitivity to oxazolone and the plaque forming cell response of splenic lymphocytes to sheep erythrocytes. Neither of the doses of Septilin altered weight gain, absolute lymphocyte counts, or host resistance against E. coli sepsis. The higher dose of Septilin reduced phagocytic activity of the PMN cells/reticuloendothelial system, but both doses increased the percentage and absolute number of circulating neutrophils, stimulated humoral immunity and suppressed cellular immunity.Thus, Septilin has dual effects on the immune system, with lower doses showing greater stimulant and higher doses showing predominantly suppressant effects. Copyright © 2002 John Wiley & Sons, Ltd.