The immunoglobulin E (IgE) antibody system is important in the genesis of asthma, but it appears to have originally evolved for defence against parasite infection. In order to study how IgE contributes to asthma, there are advantages in studying parasitized populations. Firstly, the IgE system can be studied when it is operating in a more natural state, and this could allow new insight into basic immune function. Secondly, the genetic susceptibility to produce high levels of IgE is more likely to be expressed, as the most intense IgE responses in nature are those found in the presence of parasitic infection. These more intense IgE responses should facilitate finding new 'asthma genes', assist in investigating how the DNA variations in candidate genes affect gene function and provide the possibility of developing new approaches to the treatment of asthma.