Objective. Acute focal bacterial nephritis (AFBN)or acute lobar nephronia represents an acute localized non-liquefactive infection of the kidney caused by bacterial infection. The main manifestations consist of fever, chills, abdominal pain, flank pain, and tenderness and percussion pain of the costoverbral angles. Ultrasound and CT examinations identify the renal parenchymal space-occupying lesion which may resemble renal abscess or carcinoma. The clinical symptoms and the renal,mass disappear following anti-infection treat ment. Methods and Results. Between January 1985 and May 1994, we treated 15 patients with AFBN, 10 men and five women, aged 16-56 years with an average of 30 years. The left kidneys in 11 patients and the right kidneys in four were affected. All of the patients presented a fever and persistent flank pain on affected side. Ultrasound showed local enlarged renal volume and space-occupying masses with low level echoes. CT scans demonstrated focal enlargement of affected kidneys and low-density solid space-occupying lesions. CT reconstructions showed wedge-shaped masses. 14 patients responded to appropriate parenteral antibiotics. The inflammatory masses diminished gradually in about 4 weeks. Conclusions. We believe that acute focal bacterial nephritis should be strongly suspected when a patient presents fever, chills and pain on the affected side and has a history of urinary tract infection. In addition, ultrasound and CT examinations suggest evidence of parenchymal space-occupying lesion, and the renal mass and its clinical symptoms disappear following anti-infection treatment.