[en] Velogenic strains of Newcastle disease virus (NDV) were isolated from field outbreaks. ELD/sub 50/ of the VNDV was determined at 10/sup -5.33/. La Sota strain and Incomplete Freund's Adjuvant (IFA) were inoculated in adult chicks to raise hyper immune serum. The serum was purified and used to reduce the morbidity and mortality in experimentally infected broiler chicks with Newcastle disease virus (NDV). 120 day-old broiler chicks were divided into four groups i.e. A, B, C and D. At 14 The day of age, the chicks were infected with velogenic field isolate of Newcastle disease virus (ELD/sub 50/= 10/sup -5.33/0.1mL) and two hours post infection the birds were passively immunized with HIS at the rate 2mL, 3mL and 6mL, in group B, C and D, respectively, while group A was kept as control. Chicks received 2mL HIS exhibited severe respiratory and enteric signs of Newcastle disease, while chicks received 3mL and 6mL HIS were anorexic in early days and on 10th day post inoculation (DPI) they were recovered. Gross lesions in infected birds were hemorrhages in trachea, proventriculus and intestine, and congestion in infected lungs. Histo- athological examination showed epithelial sloughing, congestion of blood vessels in group A, mild tracheitis and alveoli of lungs filled with exudates along with lymphocytes in group B, mild lymphocytic infiltration in group C, while trachea and lungs showed no significant change in group D. Higher range of GMT values were observed in group D while low range of GMT values were observed in group A. It was concluded that HIS against NDV can be used to decrease the morbidity and mortality rate in experimentally infected birds. (author)