A 1620 base pair cDNA clone showing increased expression during sucrose accumulation in leaves of Lolium temulentum has been isolated by differential screening. Comparison of the DNA sequence of the open reading frame with published sequences has revealed extensive homology with sequences coding for ATP: L-methionme S-adenosylmethionine synthe-tase, EC 188.8.131.52 (SAM synthetase) (79.6% with Arabidopsis thaliana and 81.6% with Dianthus cary-ophyllus). Increased expression was observed in both intact seedling leaves and detached mature leaves during sucrose accumulation. Expression decreased during sucrose mobilization in leaves of intact seedlings. The significance of increased expression of a gene coding for SAM synthetase during sucrose accumulation is discussed in relation to the involvement of sucrose in the regulation of plant metabolism.