AbstractTwenty one laboratory populations of the genusEnchytraeus, belonging to an unknown number of species, were investigated for 20 isozymes and unspecific protein patterns. Single specimens were used for sample preparation. The separation of proteins was performed in polyacrylamid gels by isoelectric focusing (IEF). 11 populations could be clearly differentiated from all others by their isozymes. The other 10 populations form three groups, two with each three populations and one with four. Within these groups the populations yielded identical isozyme patterns with respect to all enzymes studied. The two three‐population‐groups differed from each other only in three out of the 20 enzyme systems, while some of the other populations showed patterns of their own for all enzymes and therefore can be identified by any of them. The degree of genetic similarity between the investigated populations obviously differs considerably. Furthermore, this means that not all enzymes are suited for differentiation to the same extent, some of them have more discriminating power than others. Concerning the differentiability of the populations, the general protein patterns led to the same results as isozymes. Therefore, the protein patterns can be used as diagnostic characters, which allow identification of single specimens. Crossbreeding experiments proved the species status of all differentiable populations. The lack of any polymorphism within the laboratory populations facilitated the investigations. However, it seems not very likely that polymorphism, possibly occurring in field populations, would substantially limit the suitability of isozymes or general protein patterns as diagnostic charact