The magnitude of the diffuse leakage of metals (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn) from Finnish acid sulfate soils (AS soils) into streams was assessed and then compared to the metal discharges in effluent from Finnish industry, The diffuse leakage was calculated by using median metal concentrations for a total of 30 ditches draining AS soils and the mean annual runoff from such soils. In comparison to the present-day industrial discharges, AS soils are a massive supplier of Al, Cd, Co, Mn, Ni, and Zn to the aquatic environment. Also Cu exists abundantly in runoff from such soils, while Pb, Cr, Fe, As, and V in general do not. Since the AS soils are anthropogenic (developed as a result of deep ditching for farming purposes), the comparison with industry is justified and shows that there is an urgent need to take measures against the extensive metal leakage from these soils. It is likely that high quantities of metals are leached, in a similar manner, from corresponding soils distributed in many coastal plains worldwide.