Early use of CT and MRI helps to diagnose infection in immuno-compromised patients earlier and more precisely. Anti-fungal therapy can now be instituted in the knowledge that there is scan proven fungal disease and withheld when scans indicate other pathology. The optimal way to utilise these tests is described. Curr Opin Infect Dis 11:431–436. 1998 Lippincott-Raven Publishers