A total of 1035 household dogs were examined for the presence of Giardia lamblia (G. lamblia) in their feces. Fecal samples from 151 (14.6%) of the dogs were positive for Giardia. The protozoan was more often detected in soft feces (26.4%) than in normal (10.0%) or diarrheic feces (13.7%) (p< 0.001 and p<0.01, respectively). The forms of the organisms obtained from the 151 dogs were cysts (77.5%) , trophozoites or both cysts and trophozoites (12.6%) . Dogs kept indoors had a higher prevalence

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... 8.5%) of Giardia than dogs kept outdoors (4.8%) (p < 0.001) . Giardia infection was also more prevalent in 1-6 months old puppies (21.7%) compared to other groups (2.4%-7.5%) (p< 0.001). The prevalence of Giardia in dogs originally purchased from pet shops or breeding kennels was extremely high (21.5%) compared to that of dogs from individual households (4.3%) (p< 0.001) . With regard to human public health, the high infection rate of Giardia in puppies and dogs kept indoors is a serious problem because G. lamblia in infected dogs may have zoonotic potential. No reports of human giardiasis transmitted from dogs have been made. However, the results of this study suggest that the risk of Giardia transmission from household dogs to humans is not negligible. Pet owners should be taught appropriate hygiene measures to prevent Giardia transmission from dogs to humans.