The present invention describes novel oligonucleotides targeted to nucleic acid sequences derived from Cryptosporidium organisms, and Cryptosporidium parvum organisms in particular, which are useful for determining the presence of Cryptosporidium organisms in a test sample. The oligonucleotides of the present invention include hybridization assay probes, helper probes and amplification primers. The present invention further describes a novel method for obtaining purified ribonucleic acid from viable oocysts.