Immune responses that occur in the context of human infectious and inflammatory diseases are usually studied by sampling cells from peripheral blood, from biopsies, or by end-point harvests at necropsy. These approaches are likely to yield information that is incomplete and/or non-representative. Here, we report the development and validation of a non-invasive method to localize and to quantitate the disposition of specific subpopulations of cells in vivo. In a murine model of dextran sulfate sodium (DSS)-induced colitis, CD4+ T cells were visualized in the colon by single photon emission computed tomography (SPECT-CT) after injection of monoclonal, non-depleting, indium-111 (111In) labeled anti-CD4+ antibodies. The SPECT-CT colon uptake ratio (CUR) was found to correlate (p<0.01) with the number of total CD4+ T cells and with standard measures of pathology (colon length, cell counts, and histopathologic evidence of apoptosis, edema, and cellular infiltrates) as assessed by direct examination of diseased colon. Each of these parameters, including the SPECT-CT signal uptake, increased as a function of DSS dose (p<0.05). We conclude that CT-SPECT imaging using an 111In-labeled anti-CD4+ antibody is reflective of traditional parameters of pathology in this experimental model of murine colitis. This approach should be readily applicable to the imaging of discrete cell subpopulations in non-human primates and in humans, thus augmenting our understanding of infectious diseases and inflammation in vivo.