Neonates have quantitative as well as qualitative deficiency in their humoral immunity. Because of low level of antibody and complement in neonates there is defective generation of chemotactic factors and abnormalities of opsonisation which makes them prone to various bacterial infections. Quantitative estimation of serum immunoglobulins IgG, IgM, IgA and serum complement component C3 in cases of clinically diagnosed neonatal septicaemia cases may help in finding out the abnormalities in the humoral immune response. Quantitative estimation may be used as marker to support the diagnosis and assess response to treatment. It may also help to study the role of intravenous immunoglobulins along with the antibiotics in the treatment of septic neonates.