Bob was right.

During his career Bob Brent has been instrumental in developing the methodology to use in determining whether an exposure in pregnancy has a harmful effect on the fetus. Experience has also shown the importance of using this approach to determine when an exposure is not teratogenic. Unfortunately, the attendant debate, as illustrated in two examples reviewed, exogenous sex hormones and Bendectin, requires persistence and a thick skin. Bob has recorded in several publications how he carried out these systematic analyses. This literature will be a very valuable legacy.