Study of air pollution indicates that minute particles may adversely interfere with pregnancy and fetal development. As engineering of nanoparticles have emerged, so has concern that these might interfere with reproductive and developmental functions. This is because nanotechnology may potentially increase the overall particle burden in air and introduce particles with novel characteristics and surface reactivity. To evaluate safety for pregnant women, we have studied developmental toxicity of engineered nanoparticles (ENPs), following exposure of pregnant mice by inhalation (ENPs of titanium dioxide and carbon black), or by intratracheal instillations (multiwalled carbon nanotubes). Our findings indicate that ENPs may introduce physiological changes in organ function in the offspring that manifest in life after birth, rather than fetotoxicity and malformations. Especially the nervous, immune, and male reproductive systems seemed sensitive to insult due to maternal exposure to ENPs during pregnancy at exposure levels close to common 8 hr time weighted occupational exposure limits. It follows that the potential for developmental hazard warrants characterization. At present, the applied methodology does not always reflect state-of-the-art and the diversity in study designs hampers deduction of general rules as to developmental toxicity. Also, functional outcomes (other than male reproductive function) are rarely addressed in developmental studies of industrial chemicals. Taking into account that production and application of nanomaterials are expected to increase, a testing strategy for NP should be established.