A total of 13 new Giardia isolates were established in axenic culture. All of the new isolates were obtained by excystation of Giardia cysts from the feces of patients in Dutch hospitals. These isolates were subjected to isoenzyme and DNA analysis together with isolates from Poland, Belgium, and various other parts of the world. Isoenzyme analysis revealed that nearly all of the newly established isolates exhibited unique zymodemes. Isolates obtained from individuals from Belgium and Poland, on the other hand, displayed single zymodemes. Genomic DNA libraries were constructed from isolates belonging to the latter two zymodemes; specific and common recombinant DNA clones were selected from these libraries. Differential screening revealed that the two isolates had only 80% of the clones in common. Restriction-fragment-length polymorphism analysis using three different probes together with two synthetic probes that are complementary to Giardia structural protein genes led to the separation of all isolates into two major groups; within these groups, a further division could be made by application of other techniques or probes. The results of DNA analysis and zymodeme classification were in general agreement; in the present report they are compared with the data in the literature and discussed.