Human health risk assessments of boron (B) should evaluate this trace element's potential to impact public health at high exposure levels, while accounting for its potential nutritional importance for humans. Boron, an essential plant micronutrient, occurs naturally in the environment. Fruits, vegetables, legumes, and nuts are rich dietary sources of boron. Recent risk assessments of boron have used the rat developmental toxicity study as the pivotal study; the no-observed-adverse-effect-level (NOAEL) and benchmark dose, based on decreased fetal body weight (the most sensitive endpoint), were determined to be 9.6 and 10.3 mg B/kg/day, respectively. A reduced interspecies uncertainty factor is scientifically justified since the pharmacokinetics and pharmacodynamics of boron are similar across species. For example, major sources of pharmacokinetic variation are eliminated since boron: is rapidly distributed throughout body water, does not accumulate, is not metabolized, and is excreted primarily in the urine. With respect to pharmacodynamics, the toxicity profile of boron is similar across species; developmental and reproductive toxicity are the most sensitive endpoints of toxicity, with effects seen at similar dose levels across species. Several recent scientific risk assessments of boron in the U.S. and Europe have used reduced total uncertainty factors of 101.5. Based on a total uncertainty factor of 101.5 and a NOAEL of 9.6 mg B/kg/day, an acceptable daily intake (ADI) of 0.3 mg B/kg/day may be calculated. For a 60 kg women, this amounts to an ADI of 18 mg B/day. This ADI is well above any currently recommended minimum nutritional requirement for boron. Human exposure to boron in diet and drinking water, the two primary sources of exposure, appear to be well below this ADI. © 1997 Wiley-Liss, Inc.