pLVX-EF1α-mCherry-N1 is a lentiviral expression vector that can be used to generate high-titer lentivirus for transducing virtually any dividing or nondividing mammalian cell type, including primary and stem cells. The vector allows a gene-ofinterest to be fused to the N-terminus of the red fluorescent protein mCherry. Expression of the fusion is driven by the human elongation factor 1 alpha (EF1α) promoter, which continues to be constitutively active even after stable integration of the vector into the host cell genome. Stable expression of the fusion allows the monitoring of a variety of cellular processes (such as differentiation in primary or stem cells) without the transgene silencing associated with CMV promoters. In addition, the vector allows efficient flow cytometric detection of stably or transiently transfected mammalian cells expressing mCherry fusions, without time-consuming drug and clonal selection.