The experiment was carried out with S. Pullorum in hens and cocks. In this investigation a total of 40 pullets (later called hens; seronegative to Salmonella Pullorum) of Isa Brown breed of 18 wks and 10 cocks (seronegative to Salmonella Pullorum) of RIR breed of 26 wks age were used. The birds were divided into two groups in which one group served as control. Twenty hens and 5 cocks were kept together and experimentally infected by the oral route with 2 ×107 (CFU) dose of Salmonella Pollurum organisms in at 21 weeks of age in hens and 29 weeks in cocks while (20 hens and 5 cocks kept together) in control birds no bacteria was given. The used methods were observation of clinical signs, gross pathology, and reisolation of S. Pullorum from different organs and blood, histopatholocal study, detection of antibody levels and detection of S. pollurum by PCR at different time intervals of experimental period. Five birds (four hens and one cock) randomly selected and sacrificed on 6 hrs before inoculation and 1 wk, 2, 3 and 4 weeks of post infection (PI). A total of 20 hens and 5 cocks were used for the control group and 5 (4 hens and 1 cock) birds were necropsied simultaneously with the time schedule of the experimentally infected groups. The bacteriological samples (crop, liver, lung, heart, cecal content, blood, bile, spleen, ovary, oviduct, uterus and vagina); serum samples for ELISA and rapid plate agglutination (RPA) test; liver, lungs, heart, spleen, intestine, kidney, ovary and testis etc. for histo-pathological examination; and liver lungs, ovarian folictes and testis were collected in 50% buffered glycerol and preserved in -800C for PCR. The clinical signs of infected hens were found at 72 hrs of PI and found up to 4 weeks. These were 60% depression, 60% loss of appetite, reduced significantly mean feed intake (p˂0.01) and mean body weights (p˂0.01), 20% diarrhea, 12% emaciation and 15.81% reduced egg production. 100% liver, lungs, duodenum, ceca and spleen were positive for S. Pullorum at 1 wk to 4 weeks PI. The Salmonella Pullorum was reisolated from 81.25% crop, 93.75% liver, 87.75% heart, 100% lungs, 100% spleen, 100% ceca, 18.75% bile and 75% kidney during the study period. The highest mean CFU/ml of Salmonella Pullorum from blood was 13.55 × 103 at 1 week PI and the lowest was 13 × 102 at 4 weeks PI. Gross lesions were variable in different birds in different time interval. The highest gross lesion was 93.75% spleen swollen and congested and the lowest lesion was 56.25% necrotic foci in the liver. Microscopically, the liver showed (81.25%) congestion; hepatitis , infiltration of inflammatory cells and focal necrosis with multifocal infiltration of histiocytes in (56.25%) liver parenchyma and nodule formation with the infiltration of heterophils, lymphocytes, macrophages and plasma cells in (12.5%) liver. In rapid plate agglutination test the positive result was found from 1 wk PI with the sera of infected birds. The overall seropositive was 80% in hens. The antibody titers of infection group increased significantly (p˂0.01) in hens and cocks. The antibody titre increased gradually and the highest titer was at 4 weeks PI in hens (4712±1851) than cock (3059±903). S. Pullorum was detected by PCR in all livers, lungs and ovarian follicles from 1 week to 3 weeks PI. S. Pullorum was reislated from ovary (100%), ovarian follicle (97.75%), oviduct 68.75%), uterus (56.25%) and vagina (75) of female reproductive organs after experimental infection. S. Pullorum was reisolated from 50% eggs of experimentally infected birds. The mean egg production differed significantly (p˂0.01 and p˂0.05) in infected hens. Twenty percent hatchability was lost due experimental S. Pullorum infection. Piped chicks were 20% and embryo mortality was 15%. S. Pullorum was isolated from 66.66% chicks. In cocks, the mean feed intake and mean body weights of cocks differ significantly (p˂0.01) between infected and control group. Grossly, pericarditis, haemorrhagic and congested liver, congested and caseous lungs and white foci in the testis were observed in cock at 2 wks PI. The mean weight of testes reduced significantly (p˂0.05) in infected cocks. Histopathologically, degeneration and necrosis of spermatogonia, and infiltration of heterophils, lymphocytes and plasma cells in the somniferous tubules of testes were (75%) found. Seventy five percent testes were positive for S. Pullorum by culture and biochemical test. S. Pullorum was detected by PCR at 1 week to 3 weeks PI from testicular tissues.