Our work aims to understand the structure, assembly and function of biological macromolecule complexes. We embed unstained, unfixed specimens in vitreous ice to preserve their structures. Transmission cryo-electron microscopy is then used to visualize the specimens, but the images recorded are difficult to interpret because they are projections of the specimen degraded by noise. Thus we computationally combine images of the specimen viewed from different angles enabling us to reconstruct a three-dimensional model. Any inherent symmetry present in the structure is also used in this averaging. This method is particularly useful for objects that are too large, unstable or variable to be studied by X-ray crystallography or NMR, such as enveloped viruses.