The present study describes the pathological and bacteriological findings and diagnosis by immunoperoxidase and immunofluorescence methods in budgerigars (Melopsittacus undulatus) naturally infected with Salmonella gallinarum obtained from three commercial budgerigar rearing farms. The course of the disease in young budgerigars was peracute or acute, whereas in adult budgerigars the disease was acute or chronic. Clinically, yellow-white diarrhoea was observed in the young budgerigars with the acute form. In the adult budgerigars with the acute and chronic forms, a decrease in feed and water consumption with loss in body condition together with greenish-yellow diarrhoea was generally noted. Peritonitis and pericarditis were the most common findings in young budgerigars at necropsy, while in adult budgerigars scattered grey-white necrotic foci were found in the livers. Histopathologically, the lesions in young budgerigars were characterized with fibrinonecrotic peritonitis and/ or pericarditis and necrotic hepatitis. In adult budgerigars with acute infection, hepatic necrosis with focal heterophil infiltration was present; whilst lesions in the chronic cases were granulomatous in nature with the infiltration of macrophages, lymphocytes and histiocytes. For the detection of S. Gallinarum in formalin-fixed, paraffin-embedded tissues, the avidin-biotin peroxidase complex and immunofluorescence methods were used. Both methods showed bacteria to be localized in the liver, kidney, peritoneum, heart, spleen and intestines of both young and adult budgerigars. The results of the present study indicate that the avidin-biotin peroxidase complex method was more sensitive than the immunofluorescence method in the detection of the bacteria.