Abstract
Giardia parasite is prevalent endemically in Taif city. Infection is more prevalent in children under 5 years old and elderly people. The sickness is more intense in immune-compromised people. The disease is usually diagnosed by stool examination by the microscope, for the identification of the both trophozoite and cyst stages. Usually the disease is overlooked during stool analyses due to the minute size of the parasite and due to the scarcity of infection sometimes. Hence molecular characterization or diagnosis is used as an alternative method for the diagnosis of infection. Molecular characterization is based on polymerase chain reaction (PCR). This technique is regarded as a highly sensitive and accurate method of diagnosis. The prevalence of Giardia duodenalis was 15% in stool samples collected from different hospital in Taif. By means of RAPD technique, most G. duodenalis isolates were genetically similar, forming two main groups, with about 60% of similarity one another.