The product of the Escherichia coli secM gene (secretion monitor, formerly gene X), upstream of secA, is involved in secretion-responsive control of SecA translation. In wild-type cells, SecM is rapidly degraded by the periplasmic tail-specific protease. It is also subject to a transient translation pause at a position close to the C terminus. The elongation arrest was strikingly prolonged when translocation of SecM was impaired. SRP was not required for this arrest. Instead, the nascent SecM product itself may participate, as the arrest was diminished when it incorporated a proline analog, azetidine. We propose that cytosolically localized nascent SecM undergoes self-translation arrest, thereby enhancing translation of secA through an altered secondary structure of the secM-secA messenger RNA.