Health is an important factor affecting performance, uniformity, and shelf life based on resistance to disease. Many antibodies are found in body fluids and interstitial spaces and have the most effects on removal of extracellular pathogens such as bacteria and parasites [1]. One of the alternative ways to balance the immune system is creating a natural resistance to disease. Medicinal plants and phytobiotics which are products derived from medicinal plants, have such features naturally [2]. Harmala with the scientific name of Peganum harmala is a perennial and non fluff plant from the family of Nitrariaceae. Seeds from this plant are rich in carbohydrates, lipids, proteins, minerals, alkaloids and amino acids. Dried harmala seeds contain 35% protein, 17% oil and Harmaline, Harmine, Harman, Harmalol, Peganin, Isopeganin, Dipeganin, Vasizin and Vasyzinun alkaloids [3]. Alkaloids, Flavonoids and anthraquinones are the main phytochemical compounds of harmala. It has been reported that dietary inclusion of harmala seed and extract enhanced immunological responses of broiler chicks to sheep red blood cell (SRBC) antigen [4]. In this study, 288 one-day old Ross 308 broiler chicks were randomly assigned to 4 treatments and 4 replicates of 18 birds in each. The experimental treatments were control (diet with no feed additive), diet containing 0.02% Virginiamycin as growth promoter antibiotic, diet containing 0.25% harmala seed powder and diet containing 0.50% harmala seed powder. At 25 and 31 days of age, 1 ml of 5% SRBC suspension was injected to thigh muscles of two birds from each experimental unit and at 31 and 37 days of age, blood samples were taken from the same two birds of each cage via wing vein for determination of primary and secondary responses to SRBC, respectively. The data were analyzed in a completely randomized design using GLM procedure of SAS. Comparison of means was conducted by Duncan's multiple range rest. The results of this study showed that the pri
