We analyzed the expression pattern of transforming growth factor-beta isoforms (TGF-beta1, TGF-beta2 and TGF-beta3) in the developing brain of embryos derived from the normal and diabetic mice exposed to cyclophosphamide (CP), a cytotoxic teratogen. The CP-treated diabetic embryos showed significantly more TGF-beta1 and TGF-beta2 immunoreactive cells in the regions of telencephalon and diencephalon in comparison to that of CP-treated non-diabetic embryos. Moreover, no cells expressing TGF-beta isoforms were detectable in the developing brain of normal and diabetic embryos. The mRNA expression levels of TGF-beta isoforms were found to be significantly increased in the developing brain of CP-treated diabetic embryos compared to that of CP-treated non-diabetic embryos as measured by quantitative real time reverse transcription-polymerase chain reaction. The enhanced expression levels of TGF-beta isoforms appear to be associated with the increased frequency of neural tube defects observed in the diabetic embryos exposed to CP.