wo hundreds and ten one day hubbard chicks were used in this study. They were divided into 6 group was kept as control. The second group was experimentally infected with 0.2 ml of broth containing 10¯8 C.F.U. of S. pullorum given orally and left as positive control. The third group was experimentally infected orally with S. pullorum and intramuscularly injected with gentamicin ; 5 mg/kg b.wt. for 5 successive days.The fourth group was experimentally infected with S. pullorum and injected I/M with spectinomycin 20 mg/kg b.wt. twice with one day apart. The fifth group was injected I/M with gentamicin in the same dose regimen, while sixth group was I/M trated with spectinomycin 20 mg/kg b.wt. twice with one day apart. Non infected and gentamicin treated birds demonstrated significant increase in the total leucocytic count and serum total proteins. While treatment of infected birds withspectiomycin elicited a significant decrease in total leucocytic count. Non infected and spectinomycin treated birds divulged no significant changes in the total leucocytic counts . Both gentamicin and spectinomycin exerted more inhibitory effect on S. pullorum compared with other aminoglycosides, colistin and tetracyclines but less potent compared with chloramphenicol and enrofloxacin. It was concluded that both gentamicin & spectinomycin devoid any significant effects on chicken immune system turned by S. pulorum infection and high efficacy of both drugs either In vivo or In vitro