The diagnostic properties of several assays on live animals were studied using data from different experiments. These experiments involved 128 classical swine fever virus (CSFV) infected pigs (weaner pigs, fatteners and sows). Since all pigs in the study were infected with CSFV, only the proportion of test positive results and the time until a test positive result is obtained were evaluated. The RT-nPCR detected the highest proportion of infected pigs (98.9%), whereas the Antigen ELISA gave the worst detection results (74.7%). Within the group of test positive animals, infection was detected earliest using the leukocyte count and latest using Antigen ELISA. Using the virus neutralisation test, antibodies against CSFV were detectable on average 7.6 days after the onset of viraemia in virus isolation in whole blood. Using survival analysis, the time until the first positive diagnosis and the proportion of detected animals were combined in one test. Results showed that RT-nPCR performed significantly better than either virus isolation in different blood fractions or antigen ELISA. It is concluded that the RT-nPCR technique is the best diagnostic tool available for early detection of a classical swine fever infection.