The purpose of the present work is to set focus on the importance of built-in validation of diagnostic methods in zoonoses-surveillance programs. Appropriate and ongoing evaluation schemes are preconditions for estimating true prevalences of zoonotic infections or infestations. Estimates of true prevalences are crucial for optimizing surveillance programs so they are both cost effective and provide the best possible tool for assessing consumer safety. Using 3 examples we illustrate some of the diagnostic challenges in zoonosis surveillance that potentially could be met by appropriate validation schemes and knowledge about the performance of the diagnostic methods. We recommend that estimates of within and between laboratory variation, analytical and diagnostic sensitivity and specificity are made accessible in the public domain as part of a quality-assurance system for diagnostic methods in surveillance programs. Furthermore, we recommend that diagnostic methods be subject to an ongoing validation in any surveillance program.