The invention provides a novel human Mab Fab, cloned by phage display, and its use in diagnostic and therapeutic methods. In particular the invention provides a method for analyzing the OxLDL components of atherosclerotic plaques in vivo and a means to determine their relative pathology. As the method is based on a human Fab rather than a mouse Mab, the progress or regression of the disease may be monitored over time. The antibody may also be used for the analysis of surgical or serum samples ex vivo for the presence of OxLDL. The antibody may also be used to target therapeutic agents to the site of atherosclerotic plaques or may have use as a therapeutic agent itself.