In the Enchytraeidae, species separation and identification is often problematic due to high morphological similarity of closely related species and considerable intraspecific variability of crucial characteristics. Immature specimens are almost undeterminable. To meet these difficulties, this paper recommends the consulting of general protein patterns as exhibited by non-specific silver-staining after isoelectric focusing. A method is presented which allows the successful inclusion of protein data in taxonomic studies and field surveys. Two examples from an investigation on Fridericia field populations show that, with the help of general protein pattern analysis, a clear taxonomic decision on the identity of morphologically aberrant forms and of juvenile specimens as well can be achieved with comparatively little expenditure of time. A combined use of morphological and protein data for taxonomic purposes is suggested.