Scanning tunnelling microscopy (s.t.m.) has been used to study the structure of the non-crystalline globular protein vicilin. Molecules were deposited on amorphous carbon substrates and imaged both in air and in vacuo without additional sample preparation. Current-voltage plots of an individual protein molecule are also reported. The s.t.m. images are compared with conventional transmission electron micrographs and with a model of vicilin based on small-angle synchrotron X-ray scattering data. © 1989.