Infectious bronchitis virus (IBV) is the causative agent of avian infectious bronchitis, which is characterized by respiratory, reproductive and renal signs. Two IBV samples, which were isolated from commercial chickens with respiratory disease (USP-78), and severe enteric disturbs and mild respiratory disease (USP-22) were inoculated in 26-day-old chickens and characterized by partial sequencing of the S1 gene. The sample USP-22 was inoculated by the oral and oculonasal routes (group 1 and 2, respectively) and the sample USP-78 was inoculated by the oculonasal route (group 3). The three groups showed similar clinical signs and microscopic lesions. The clinical signs included depression, coughing, sneezing, tracheal rales, open mouth breathing and mild watery faeces. The macroscopic and microscopic lesions were more evident in trachea. The nucleotide sequences revealed 98.3% identity between the both field isolates and between 52.5 to 76% identity when they were compared with vaccine strains available worldwide.