In five floodplain transects along the course of the river Tarnava Mare in Rumania, 17 earthworm species werecounted. The species spectrum of the earthworm fauna of the studied floodplains is dependent on the provenance of thefloodplain sediments. On the basis of this provenance, the fauna of three groups of soil localities on the floodplain aredifferentiated: in the upper reaches of the river, the fauna of the floodplain soils derived from brown forest soils and podzolicsoils (near Sub Cetate); on the eastern side of the middle reaches, the fauna of the soils mainly derived from gray-brown podzolicsoils (near Porumbenii Mari, Hoghilag); and on the western side of the middle reaches and the lower reaches, the fauna of thesoils principally derived from planosols (near Alma, Valea Lung ). Proctodrilus tuberculatus occurs in the floodplain sedimentspredominantly derived from the gray-brown podzolic soils, and in those parts of the floodplain derived from planosols P.opisthoductus and Aporrectodea georgii are found. Ap. georgii and Allolobophora leoni are mostly mutually exclusive in thefloodplain transect, were they are apparently indicator species of sediment deposition close to the river and/or the effect of highwater on the soil chemistry. P. tuberculatus and P. opisthoductus occur as vicarious species in the soil profile of the area wheretheir distribution overlaps. Three soil factors that are significant in determining earthworm distribution are emphasized:lessivage, or translocation of clay; the pervection of colloidal organic matter (humus) into the soil, and the texture of the soillayers resulting from sedimentation. An additional record of the new species P. thaleri is given.