The occurrence of an infectious chicken disease, the Avian Nephritis was suspected to be present in Hungary from the early ‘70es, but the evidence was provided by a PCR based diagnostic method developed recently. The infectious nephritis is a component of the so called “baby chick nephropathy”, referring to the localization and early appearance of the symptoms. The chickens from the third day after hatching develop diarrhea and weakness following per oral infection: retarded growth is observed from the second week post infection. The mortality is usually low, except those cases where the tubular epithelium of the kidney is damaged due to the virus replication, nephroso-nephritis develops and the regressive changes result in uricosis (gout). The loss of the disease may be decreased or prevented if predisposing factors (such as keeping problems or malnutrition) are recognized and eliminated.