Questions have been raised recently about the ethics, safety, and effectiveness of generic substitutes for brand-name products. To address this issue, the FDA has examined all 127 in vivo bioequivalence studies in the 273 generic drug applications approved in 1997. The examinations focused on data that are used to evaluate the therapeutic equivalence of a generic and innovator drug. Three measures were reviewed: the area under the plasma drug concentration–time curve from time 0 to time t (AUC [0-t]), the AUC from time 0 to infinity (AUC [0-Inf]), and the highest drug concentration (Cmax). The observed mean difference between the innovator's product and the generic product for AUC (0-t) was ± 3.47% (SD, 2.84), for AUC (0-Inf) it was ±3.25% (SD, 2.97), and for Cmax it was ± 4.29% (SD, 3.72).