Acute Phase Proteins (APPs) are a special type of protein created by the liver when the body mounds an immune response to infection. The University of Bonn, in the framework of a LIFE QUALITY project, investigated the use of APP levels in the bloodstream as an indicator of the health of pigs. The challenge for pig farmers is identifying whether their herd is at risk or not. It is neither feasible nor economically sensible to test all members of the herd, therefore small representative groups must be sampled. During the three-year tenure of the project, the German researchers identified several key constraints that must be kept in mind when sampling. As in all controlled experiments, the potential interference of other variables that influence health, such as age, sex, size or status, must be eliminated. Sample size should not dip below ten animals and the pigs should be selected at random from different pens. Ideal ages and weights of the animals to be sampled have been defined. The University of Bonn scientists found that simply averaging the APP level over the group could be misleading. Additional indicators of statistical significance, such as the standard deviation or error, are essential. Another trap that the farmers must avoid is sampling following vaccinations since the subsequent high APP levels will falsely indicate sickness. Predictive power can be improved by supplementing the APP measurements with other biological tests of the animals, such as serum profiles. APP testing could also be used before and after implementing health-related improvements, thereby gauging the effectiveness of the measures taken. Following these guidelines, the pig farmers can be confident that they will make the right decisions when it comes to their herd's health. For instance, when APP levels exceed a predefined threshold, the herd should be tested immediately for infectious diseases. Pig farmers and others interested in learning more about this work should visit the project web site at: http://www.gla.ac.uk/appinpigs/.