A number of plasmids were constructed containing chimeric genes consisting of fragments of antisense-oriented lentil lipoxygenase cDNA. The different constructs were tested for their ability to lower lipoxygenase activity in lentil protoplasts. Plasmids containing a full length lentil lipoxygenase cDNA proved to be the most effective, reducing the activity of the target enzyme to 70% of the control value. On the other hand, the full length lentil lipoxygenase cDNA in the sense orientation yielded a 20% increase of lipoxygenase activity.