In six patients with suspected infection, scintigraphy with diffusible tracers outlined the margins and central portion of an abscess. An animal model was developed to study this process quantitatively. Small inflammatory lesions yielding volumes of pus of 0.1-0.2 mL were shown to have increased blood volume of 0.7 +/- 0.5 mL, increased blood flow by a factor of three and increased extracellular fluid volume of 10 +/- 6 mL. This supports the patient data and indicates that the pathophysiologic features characterising the clinical studies are hyperemia and oedema associated with an abscess. The slow, central area of tracer diffusion corresponded to the presence of pus. Scintigraphy with 99mTc-DTPA is a convenient way of detecting suspected inflammatory lesions and localising collections of pus.