Ovalbumin challenge models of asthma offer many opportunities for increasing our understanding of the pathogenetic mechanisms underlying this disease, as well as for identifying novel therapeutic targets. There is no single "classical" model, because numerous alternatives exist with respect to the choice of mouse strain, method of sensitisation, route and duration of challenge, and approach to assessing the host response. Moreover, the limitations of these models need to be recognised when attempting to interpret experimental findings. Nevertheless, careful use of well-defined models allows investigators to answer specific questions that are otherwise difficult to address.