Accurate diagnosis is critical for effective treatment of the invasive infection by Candida albicans. Here, we investigated whether a (99m) technetium (Tc)-labeled Fab' fragment of the monoclonal antibody specific for the C. albicans germ tube could specifically identify an invasive C. albicans infection. The germ tube of C. albicans was used as an immunogen to obtain monoclonal antibodies and the Fab' fragment of MAb03.2 C1-C2 with highest affinity and specificity was labeled with Tc-99m. In vitro binding assays showed that the labeled Fab' preferentially bound to the germ tubes of C. albicans (4.23 +/- 0.17 x 10(2) Bq per 1 x 10(7) cells). These values were significantly higher than those for blastospores of C. albicans, blastospores of heat-killed C. albicans, Aspergillus fumigatus, Staphylococcus aureus, and Escherichia coli (P < 0.05). By using in vivo biodistribution and planar imaging with single photon emission computed tomography, we demonstrated a significant specific accumulation of radioactivity in C. albicans-infected tissues. In summary, Tc-99m-MAb03.2 C1-C2 Fab' is able to specifically accumulate in C. albicans-infected tissues, but not in tissue infected with A. fumigatus or bacteria or in a sterile inflammation. This study provides a new and specific radiopharmaceutical for the diagnosis of invasive C. albicans infections.