We have fused the promoter of the shrunken gene isolated from Zea mays to the bacterial neomycin phosphotransferase II gene from Tn5. The plasmid construction pSKAN1 was used for transformation of a Triticum monococcum suspension cell line. Expression of the chimaeric gene was analysed a short time after transformation by estimating neomycin phosphotransferase II activity. Maximum enzyme activity was found 4 days after transformation but activity could still be detected after 10 days. The conformation of the introduced plasmid DNA changed from supercoiled towards the open circular and linear forms within the plants cells; only the latter could be detected 10 days after transformation. As the majority of foreign DNA introduced into the Triticum monococcum cells remained extrachromosomal, transcription probably occurred from the extrachromosomal plasmid copies. This transient gene expression was dependent on the presence of the promoter fragment of the Shrunken gene and suggests that a promoter isolated from Zea mays can act in Triticum monococcum cells.