Three methods of isolating Cryptosporidium parvum oocysts from rat feces were evaluated. Oocysts were initially isolated by sucrose density gradient centrifugation. They were further purified by passage through a glass bead column or a Percoll gradient or by dialysis. Although oocysts recovered from the glass bead column and by dialysis were relatively free of fecal debris, only oocysts recovered from the Percoll gradient were free of bacteria. Recovered oocysts retained their antigenicity and infectivity. The ability to effectively recover oocysts from rat feces suggests that the laboratory rat may be a convenient substitute for ruminants in the propagation and maintenance of C. parvum oocysts for in vitro and in vivo use.