Unlike cell lines, human hematopoietic stem cells (HSCs) are less efficiently transduced with HIV-1 vectors, potentially limiting this approach. To investigate which step (internalization, reverse transcription, nuclear transport, and integration) limits lentiviral transduction, we evaluated the kinetics of lentiviral transduction in human CD34+ cells. We transduced HeLa and CD34+ cells with self-inactivating HIV-1 vector at low and 10-fold higher MOIs, and evaluated vector amounts at various timepoints based upon the rationale that if a given step was not limiting, 10-fold greater vector amounts would be obtained at the 10-fold higher MOI. We observed slower internalization (>60 minutes), a peak of reverse transcription at 24 hours, and completion of integration at 3 days in CD34+ cells. In HeLa cells, vector amounts at high MOI achieved ~10-fold greater values over all timepoints. When compared to HeLa cells, CD34+ cells had a larger difference of vector amounts between high and low MOIs at 2–6 hours and a smaller difference at 12 hours to 10 days, revealing a limitation in human CD34+ cell transduction around 12 hours, which corresponds to reverse transcription. In serial measurements of reverse transcription at 24 hours, vector amounts didn’t decrease once detected among CD34+ cells. When using an HSC expansion medium, we observed less limitation for starting reverse transcription and more efficient transduction among CD34+ cells in vitro and in xenografted mice. These data suggest that initiation of reverse transcription mainly limits lentiviral transduction for human CD34+ cells. Our findings provide an avenue for optimizing human CD34+ cell transduction.