Four lambs 4 months old were inoculated with Cryptosporidium andersoni oocysts (bovine isolate) in a dose of 5 x 10(6) per animal followed later by 1 x 10(7) oocysts per animal. No animal shed Cryptosporidium oocysts during 56 days post infection, no lamb showed clinical symptoms of cryptosporidiosis and no macroscopic changes were detected in the abomasum immediately after autopsy. Histological examinations did not demonstrate the occurrence of Cryptosporidium in the abomasum and other selected organs.