Microbiological diagnosis for rheumatic diseases is increasingly used as part of the diagnostic work-up in rheumatological practice due to growing knowledge about bacteria-induced rheumatic diseases. This review's focus lies on rheumatic diseases, which in contrast to septic-infectious arthritis, are characterized by the inability to culture bacteria from the inflammed joint. These reactive arthritides occur after primary extraarticular bacterial infection. The etiological diagnosis of reactive arthritis is based on the detection of a previous or ongoing bacterial infection. Diagnosis is performed by serology or direct detection of the bacterial organism or parts thereof at the site of entry and recently by molecularbiology-based detection of the bacteria in the inflamed joint. This review reflects the current diagnostic approaches and formulates diagnostic algorithms for specific and well-directed microbiological diagnosis.