The effects of low-dose rate/low-dose intrauterine exposure during organogenesis were investigated using pregnant mice and an experimental system employing both 2-D electrophoresis and mass spectrometry. Ras GTPase-activating protein-binding protein 1 and Rho GDP-dissociation inhibitor 1 are known to play vital roles in the morphological development of the nervous system such as synaptic plasticity and elongation of axons. These proteins showed a marked increase in fetal tissues collected 3 days after mothers were administered 3.7 MBq ³³P-ATP. This suggests that active GTPase decreases and inactive GTPase increases resulting in a disruption of neurotransmission. To confirm if these changes were associated with microcephaly, PQBP1 (Polyglutamine binding protein 1) expression was determined by Western blot assay. Administration of 3.7 MBq resulted in a marked inhibition of PQBP1 expression in fetal tissues proving that even low-dose internal exposure was enough to induce changes suggestive of microcephaly. Actual measured values from the maternal injection site confirmed that the total dose over the 3 days after administration is about 50 mGy. This demonstrates that even low-dose intrauterine exposure warrants caution, suggesting that appropriate radiation safety measures such as education pertaining to the risks of exposure is important for pregnant workers.