FDA commissioner Margaret Hamburg has announced her resignation effective March 31, bringing to an end a six-year tenure that commenced at a time when the agency's device center was rocked by allegations of managerial impropriety. FDA's January appointment of Robert Califf to the post of deputy commissioner for medical products and tobacco is feeding speculation that the former cardiologist will take over for Hamburg, but several factors argue otherwise, including that Hamburg mentioned only FDA chief scientist Stephen Ostroff, who will serve as acting commissioner, in her missive to the agency.