en Infectious disease (Molecular and Cellular aspects) Infectious disease (Molecular and Cellular aspects) Original Article Original Article <p> <i> Cryptosporidium </i>species are one of the most common causes of gastrointestinal infection in humans around the world. This study has aimed to investigate the hyper variable region of the 18S rRNA gene in <i>Cryptosporidium</i> for exact parasite identification . </p><p>  DNA was extracted from 26 fecal samples from which initially <i>Cryptosporidium </i>oocysts were identified by Ziehl-Neelsen acid-fast , Auramine phenol and ELISA techniques. Nested PCR, targeting the most polymorphic region of the 18S rRNA gene and genotyping was performed by restriction endonuclease digestion of the PCR product followed by nucleotide sequencing and phylogenic analysis. </p><p>  Among 26 isolates analyzed, three species of <i>Cryptosporidium </i>were identified 38.5% of the isolates were <i>C. hominis</i> while 53.8% of the isolates were <i>C. parvum</i> and 7.7% of the isolates were <i>C. meleagridis</i>, which the last two species have the potentially zoonotic transmission. The only 11T subtype of <i>C. hominis</i> was demonstrated. These strains clustered distinctly into either human or animal origin regardless of the geographical origin, age, or immunity status of the patients. </p>In summary, this work is the first report of <i>C. meleagridis </i>infecting human in Iran. Moreover, it suggested that multi-locus study of <i>Cryptosporidium</i> species in developing countries would be necessary to determine the extentof transmission of cryptosporidiosis in the populations. 18S rRNA, Cryptosporidium, diarrhea, developing countries 153 161 http://ijmcmed.org/browse.php?a_code=A-10-87-1&slc_lang=en&sid=1 Salman Ghaffari s3ghaffari@yahoo.com 10031947532846002299 10031947532846002299 No Parasitology and Mycology Group, Faculty of Medicine, Babol University of Medical Sciences, Babol, Iran. Narges Kalantari nfkala@gmail.com 10031947532846002300 10031947532846002300 Yes Cellular and Molecular Biology Research Centre, Babol University of Medical Sciences, Babol, Iran.