A new laboratory animal model for experimental cryptosporidiosis is described. Adult immunosuppressed hamsters were infected per os with 0.5 x 10(5) and 1 x 10(5) Cryptosporidium oocysts of calf origin. The mean numbers of oocysts shed per gram of feces per day and the patterns of infection are described. The susceptibility to Cryptosporidium infection, the total number of oocysts shed (a thousand times the infective dose), and the ease of handling in laboratory conditions make hamsters a good animal model for cryptosporidiosis.