Roe deer (Capreolus capreolus L.) is a representative of the new host of an intestinal flagellate of the genus Giardia. Giardia spp. was found during autopsy in three dead head of roe deer (roe deer calf 7-8 months, doe, buck) sent for examination to the State Veterinary Institute, Praha, from three different localities of the Czech Republik. Localization of the Giardia spp. was studied in the intestinal tract of the roe deer calf in native preparations in the intestinal contents and in the smears of intestinal mucosa stained after Giemsa (at a distance of 30-40 cm along the whole length of the small intestine). Giardia trophozoites were found in the small intestine in the section of 280-770 cm from the caudal part of duodenum. The trophozoites occurred most intensively within the section of 350-420 cm. The trophozoites showed active, motility in this part of the small intestine as late as in more than 48 hours after the death of the row calf. Their size (obtained by measuring 30 trophozoites) was from 12.4-16.2 to 8-11.5 microns with the mean of 14.5 to 9.4 microns. In the contents of the caeca and colons of all three animals after death numerous Giardia cysts were found, in the caecum of the roe calf trophozoites were detected rarely. Most of the cysts were of ovoid shape. Their size, by measuring 50 cysts from each of the animals, was from 11.2-14.4 to 8-10.4 microns with the mean of 13.3 x 9.1 microns. Sporadically, nearly spherical cysts occurred (12.8-13.6 to 9.6-10.4 microns).(ABSTRACT TRUNCATED AT 250 WORDS)