Healthspan (the life period when one is generally healthy and free from serious disease) depends on nature (genetic make-up) and nurture (environmental influences, from the earliest stages of development throughout life). Genetic studies increasingly reveal mutations and polymorphisms that may affect healthspan. Similarly, claims abound about lifestyle modifications or treatments improving healthspan. In both cases, rigorous testing is hampered by the long lifespan of model organisms like mice (let alone humans) and the difficulty of introducing genetic changes to examine the phenotype of the altered genome. We will develop C. elegans as a healthspan model. Already validated extensively as an ageing model, this organism can be readily modified genetically, and effects of environmental manipulations on healthspan can be measured in days or weeks. Once validated as a healthspan model, it can be used for an initial assessment of preventive and therapeutic measures for humans, as well as for risk identification and the initial evaluation of potential biomarkers. It will also prove useful to study interactions between genetic and various environmental factors.