en Parasitology and Mycology Parasitology and Mycology Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine Giardia lamblia cysts were isolated from fecal samples of 55 symptomatic and asymptomatic patients with giardiasis. The cysts were harvested and purified using the sucrose gradient method. IS The excystation of G. lamblia was obtained by treating them with HCI (0.01N)', then they were transferred on to modified TYI-S-33 medium. Out of 55 stool samples 17 cases were excysted with a rate of 4-32%,but we were able to cultivate only one case with 12% excystation in culture medium. The generation time of G.lamblia was calculated to be about 10.33 hours. Cryopreservation of trophozoites was successfully done in liquid nitrogen and the thawing process had a survival rate of 85-90%. 255 258 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-569&slc_lang=en&sid=1 M REZAIAN 20031947532846006004 20031947532846006004 Yes From the Department 0f Parasitology, School of Public Health, Tehran University of Medical Sciences SM GHALHARI 20031947532846006005 20031947532846006005 No the Department of Parasitology, Pasteur Institute. Tehran, Islamic Republic of Iran.