Infections of the chest and abdominal wall are rare but potentially fatal disorders that can occur spontaneously or in association with diabetes mellitus, immunosuppression, or trauma. The condition (either in the form of necrotizing fasciitis and/or pyomyositis) is difficult to diagnose clinically because of poor localizing signs. Prognosis depends on early recognition, extent of disease, and type of causative organism. Pathologically, the infections can manifest as cellulitis, abscess, and/or granulation tissue formation. To determine the value of MR imaging in the assessment of these infections, we compared the findings of MR with those of CT, sonography, scintigraphy, and plain radiography in 13 patients with proved thoracic and/or abdominal wall infection. The imaging findings were correlated with microbiological, pathologic, and/or surgical data. The isolated pathogens were Staphylococcus aureus (n = 6), Klebsiella pneumoniae (n = 1), Mycobacterium tuberculosis (n = 4), and Streptomyces somaliensis (n = 2). In 10 of 13 patients, MR imaging and CT were comparable and proved accurate in detecting the nature and extent of the inflammatory process. In seven of the patients, CT also was useful in guiding percutaneous biopsy and/or partial drainage procedures. Coronal and sagittal MR images were helpful for planning surgery. Rib osteomyelitis was missed with both techniques in one patient; in two other patients who did not have CT, MR imaging missed osteomyelitis of the ribs, the spinous process of a vertebral body, and the iliac bone. Sonography underestimated the extent of the disease in all 13 patients, but detected fluid collections in six. Findings on scintigraphy and plain radiography were the least contributory to the diagnosis and treatment of these patients.(ABSTRACT TRUNCATED AT 250 WORDS)