Equal numbers of day old White Rock and Nigerian indigenous male chicks were reared to 10 weeks of age under 4 variables consisting of 2 dietary regimes and 2 regimes of immunity (natural versus vaccinal) to Newcastle disease challenge. Although White Rock grew significantly faster, ate more food and tended to be more efficient in feed utilisation than the indigenous chicks, the mortality of the latter was significantly lower. Growth rate and feed intake were significantly greater, feed efficiency better and prechallenge mortality lower in birds fed on the higher crude protein diet. Prechallenge mortality was significantly lower in birds that had been vaccinated against Newcastle disease.