In the present article, the study to examine the ability of free-living amoebae (FLA) to serve as vectors of cryptosporidia is presented. Ten strains of different free-living amoebae of the FLA collection of the Parasitology Lab at Koblenz were cultivated in the presence of Cryptosporidium parvum oocysts. After phagocytosis and ingestion, the oocysts could be found in food vacuoles within the cytoplasm of the trophozoites of two different FLA strains. The uptake and the transport of the oocysts within the trophozoites could be demonstrated in an Acanthamoeba sp. (group II) strain (maximum, three oocysts; average, one oocyst) as well as in a Thecamoeba quadrilineata strain (maximum, 15 oocysts; average, eight oocysts), with the help of light microscopy. We found that these free-living amoebae can temporarily harbour cryptosporidia, thus supporting the suggestion that FLA may act as carriers and vehicles for cryptosporidia. However, proliferation did not take place within the host amoebae. No cryptosporidium oocysts were found within the cysts of the amoebae. To our knowledge, this is the first study to determine the "host range" of free-living amoebae as vectors and vehicles of cryptosporidia. Free-living amoebae appear able to act as carriers or vectors of the oocysts and thus may play a certain role in the transmission of cryptosporidia.