α-Santonin, a compound extracted from the flower heads of Arthemisia maritima plant, was effective in elimination of small, multicopy, relaxed plasmids (pBR322 and pBR329 with CoLE1 origin of replication in Escherichia coli, whereas plasmids of IncF1, H1 and X group were totally refractory under similar conditions, suggesting that this agent was specific in curing the CoLE1 group of plasmids.