Cruciferous vegetables are widely acknowledged to provide chemopreventive benefits in humans, but they are not generally consumed at levels that effect significant change in biomarkers of health. Because consumers have embraced the notion that dietary supplements may prevent disease, this review considers whether an appropriately validated sulforaphane-yielding broccoli sprout supplement may deliver clinical benefit. The crucifer-derived bioactive phytochemical sulforaphane is a significant inducer of nuclear factor erythroid 2-related factor 2 (Nrf2), the transcription factor that activates the cell's endogenous defenses via a battery of cytoprotective genes. For a broccoli sprout supplement to demonstrate bioactivity in vivo, it must retain both the sulforaphane-yielding precursor compound, glucoraphanin, and the activity of glucoraphanin's intrinsic myrosinase enzyme. Many broccoli sprout supplements are myrosinase inactive, but current labeling does not reflect this. For the benefit of clinicians and consumers, this review summarizes the findings of in vitro studies and clinical trials, interpreting them in the context of clinical relevance. Standardization of sulforaphane nomenclature and assay protocols will be necessary to remove inconsistency and ambiguity in the labeling of currently available broccoli sprout products.