Porcine reproductive and respiratory syndrome virus (PRRSV) is a major pathogen of swine. Due to genetic variation between the European and the US genotype as well as within both genotypes detection of PRRSV is a diagnostic challenge. This paper reports on a ring test to compare different
established reverse transcriptase polymerase chain reaction methods applied routinely in 16 different laboratories in Germany. Three different sets of samples were sent to the laboratories which were to be analysed as follows: (i) basis package: detection of PRRS (yes/no); (ii) differentiation
package I: differentiation of EU and US genotypes; and (iii) differentiation package II: differentiation of EU field isolates and EU vaccine strain. A total of 80% of the samples of the
basic package were analysed correctly, the analysis of the differentiation package I revealed 61.82% correctly tested samples and the two laboratories that analysed the differentiation package II showed only one correct result. The ring test showed that the majority of incorrect diagnoses were falsenegative results.