CA9 and neoplasm: The purpose of this study was to generate low molecular weight Fab and F(ab')2 fragments of the CAIX-targeted chimeric antibody cG250, to compare their CAIX binding affinity to that of intact cG250 and to evaluate their potential as imaging agents in a xenograft tumor model with heterogeneous CAIX expression, as a prelude to using one of these agents for clinical imaging CAIX in hypoxic tumors.