A metal-strip pickling apparatus has feed means including upstream and downstream bridle-roller pairs for longitudinally displacing the strip under longitudinal tension along a straight transport path from the upstream bridle-roller pair to the downstream bridle-roller pair. A housing longitudinally traversed by the strip is subdivided longitudinally by a succession of transverse partitions into a longitudinal succession of compartments each having a respective treatment bath, normally of acid. Each partition has a rigid lower partition half having an upper edge and an upper partition half having a lower edge portion elastically engaging the upper face of the strip moving along the path. The upper edges all are longitudinally aligned and touch the lower face of the strip moving along the path. The acid baths have liquid levels above the upper edges of the respective lower partition halves. The lower portions of the upper partition halves seal tightly with the strip and respective lower partition halves. Thus liquid from one bath cannot pass between the respective partition halves into the next compartment. The use of a straight transport path through the apparatus means that strip tension is irrelevant.