This invention relates to non-radioactive markers that facilitate the detection and analysis of nascent proteins translated within cellular or cell-free translation systems. Nascent proteins containing these markers can be rapidly and efficiently detected, isolated and analyzed without the handling and disposal problems associated with radioactive reagents. Preferred markers are dipyrrometheneboron difluoride (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes.