Azadirachta indica is the prime adaptable medicinal plant with a range of biological activities, including antidiabetic, anticarcinogenic, anti-inflammatory, antiviral, and immunostimulatory properties, known from the past 2000 years. It has been demonstrated that aqueous stem bark extract improves the in-vivo immunomodulatory response of Balb/C mice to the red blood cells of sheep. The aqueous extract of A. indica demonstrated potent anticomplementary properties that were dose and time-dependent and most prominent in an assay for the classical complement pathway. Additionally, a variation in the dosage led to a decrease in the chemiluminescence of polymorphonuclear leukocytes, while an increase was observed in the synthesis of the migration inhibitory aspect in lymphocytes. The oil from neem has been demonstrated to have immunostimulant action via specific engagement of cell-intervened immune systems to produce improved response toward future antigenic or mitogenic challenges along with immunomodulatory effects on mice. After three days of therapy, mice receiving injections of neem oil that is, intraperitoneal displayed increased leukocytic cells. Additionally, peritoneal macrophages of the mice showed increased phagocytic activity and MHC class-II antigen expression. The main active ingredient in the seed oil of A. indica, that is, nimbidin, is a mixture of tetranortriterpenes that has potent anti-inflammatory and antiarthritic properties. It does this by inhibiting some of the neutrophil and macrophage functions related to inflammatory response after exposure both in vitro and in vivo. Further investigation revealed that nimbidin also reduced neutrophil degranulation as measured by the release of lysozyme, myeloperoxidase, and glucuronidase (Kaur et al., 2004; Mehrotra et al., 2002).