To clarify activation characterization of wheat (Triticum aestivum L.) retrotransposons, transcriptionally active Ty1-copia retrotransposons were found in wheat by using RT-PCR to amplify the RT domain. Sequence analysis of random RT-PCR clones reveals that Ty1-copia retrotransposons are highly heterogeneous and can be divided into at least four groups, which are tentatively named TaRT-1 to TaRT-4.Dot blot hybridization indicates that TaRT- 1 exists in the wheat genome as multiple copies (at 30 000 copies/a hexaploid genome (ABD)). Northern blot hybridization showed that TaRT-1 is only expressed at a low level under normal conditions in seedlings, but at a high level when induced by powdery mildew fungus, jasmonic acid (JA) and salicylic acid (SA). These results suggest that the TaRT-1 expression is highly sensitive to biotic and abiotic stresses.