As it heads in a southwesterly direction the Merzalbe flows through the valley below the village of Leimen and then through Merzalben.

After 12 km (7.5 mi) it empties from the right into the Rodalb near the Riegelbrunnerhof, a hamlet belonging to Münchweiler.

Its waters then flow down the Schwarzbach, Blies, Saar and Moselle before finally reaching the Rhine.

In this document Count Frederick III of Leiningen [de; bg] was given Castrum Grebinstein and granted the villages of Merichisalbin, Rothalbin and Eiswilre.

In ignorance of this recorded origin of the name, a theory later arose that the name "Merzalb" meant "harmful / useless stream", because the first part of the name was thought to be related to the word ausmerzen ("eradicate") and thus to mean that either large amounts of water poured through the valley when the snow melted, causing damage, or that - more likely - the stream usually had too little water to be suitable for the operation of a mill.