Genetic resistance to Newcastle disease among three ecotypes of Tanzanian local chickens, Ching’wekwe, Kuchi and Morogoro MEDIUM was investigated by natural challenge with endemic velogenic strains of Newcastle disease virus (vNDV). The study was designed to determine variations in susceptibility and response to NDV among the three ecotypes. Naturally NDV-infected seeders were introduced into flocks of susceptible chickens under a controlled environment. For each bird, body weights were measured at 0, 7, 9, 11, 13, 15, 17, and 25 days post-exposure. Flock mortality was assessed every 8 hours for the first three days and then every 12 hours thereafter until 29 days post-exposure. Date and time of death was recorded, and post-mortem examinations performed for each dead chicken. Lesions on the trachea, proventriculus, intestines, and caecal tonsils were scored for severity ranging from 0 to 3. Linear models were used for survival days, post-exposure growth rate and average lesion score. Preliminary results indicate that post-exposure weight reduction in Ching’wekwe was significantly less than in Morogoro Medium and Kuchi. No significant differences were observed in the lesion scores and survival times among the three ecotypes after exposure. More data is being collected for more comprehensive analysis.