In recent years, a series of new approaches for the laboratory diagnosis of viral infections have been developed. In the present review, we describe the different tests available, such as virus isolation and identification in cell culture, antigen and genome detection, and determination of antibodies by serological methods. In order to chose the appropriate test for a given case, advantages and disadvantages of the laboratory procedures as well as their suitability for specimens taken from different organs have to be taken into account. Such considerations are particularly important for a correct interpretation of the results.