Provided herein is a method for determining the number of sites of infection of a cell culture, including the steps of: infecting a cell culture arranged in a sample carrier with viruses, counting any infected areas of the cell culture by means of a transmitted light method, marking infected cells with fluorescence markers, counting infected areas of the cell culture by means of a fluorescence analysis method, and evaluating area by area the areas determined in both methods for determining the number of sites of infection.
