While the strong biotin-avidin interaction has been widely used for the detection of biomolecules, its irreversibility complicates their isolation. We report the synthesis of a photocleavable biotin derivative (PCB) which eliminates many limitations of existing methods. This reagent contains a biotin moiety linked through a spacer arm to a photocleavable moiety, which reacts selectively with primary amino groups on any substrate. In experiments using [leucine]-enkephalin as a model substrate, we show that PCB retains its high affinity toward avidin/streptavidin and allows rapid (< 5 min) and efficient (> 99%) photorelease of the substrate in a completely unaltered form. Photocleavable biotins should be useful in numerous applications involving the isolation of proteins, nucleic acids, lipids, and cells.