We examined the control of salt excretion by leaves of the mangrove Avicennia germinans. Endogenously secreted salt on intact leaves was compared to exogenously deposited salt spray on excised leaves. Lower salt excretion was observed on seaward leaves with high salt deposition, and higher salt excretion was found on landward leaves with low salt deposition. Similar total salt loads accumulated on leaves located throughout the tree crown, suggesting that Avicennia germinans controls salt excretion at the foliar level by responding to variation in salt deposition. We propose that the salt excretion rate in leaves is a response to the gradient of salt between the xylem and leaf surface.