The present invention relates to pyrrolobenzodiazepines PBDs , in particular pyrrolobenzodiazepines having a labile N10 protecting group, in the form of a linker to a cell binding agent. The first PBD antitumour antibiotic, anthramycin, was discovered in Leimgruber, et al. Since then, a number of naturally occurring PBDs have been reported, and over 10 synthetic routes have been developed to a variety of analogues Thurston, et al. Family members include abbeymycin Hochlowski, et al. Antibiotics, 40, , chicamycin Konishi, et al.