The order Diphyllobothriidea is a unique group of tapeworms in terms of the wide spectrum of definitive hosts involving all groups of tetrapods including man. They are almost globally distributed in both freshwater and marine ecosystems, but there are also terrestrial species. It is very difficult to identify species of diphyllobothriid cestodes to the species level. Morphology of the eggs might represent a new method in the differential diagnosis of these parasites. Besides the size and shape of the eggs, the structure of egg surface might play a significant role in the determination of different taxa. For the analysis of these characteristics Scanning Electron Microscopy (SEM) was used. Experimental infections in hamsters and man were done.