Four 4-mo-old elk calves (Cervus elaphus) obtained from northeastern Oregon (USA) each were inoculated orally with 250,000 sporocysts of Sarcocystis spp., including S. sybillensis and S. wapiti. Three similar elk calves of comparable ages and weights served as uninoculated controls maintained with the inoculated elk during the experimental period between September and December 1993. Body weights were evaluated at 0 and 90 days postinoculation (PI); packed cell volumes of whole blood were evaluated at 0, 30, and 60 days PI, and numbers of sarcocysts in histologic sections from 11 selected tissues were evaluated at 90 days PI. Significant differences in blood packed cell volumes were not detected between groups (P > 0.05). Except for weight gain, elk remained healthy. Mean (+/- SE) weight gain of inoculated elk (27.1 +/- 1.6 kg) was significantly (P < 0.05) less than that of controls (40.2 +/- 4.9 kg). Mean (+/- SE) number of sarcocysts in tissues of inoculated (114.4 +/- 25.7 cm2) and controls (4.5 +/- 1.4 cm2) differed significantly (P < 0.05). Heart, esophagus and skeletal muscle contained the most sarcocysts. No sarcocysts were detected in brain, spinal cord, or testicles. Histologically, mononuclear myositis and myocarditis, with numerous intralesional sarcocysts were seen. Less severe, but widespread inflammation occurred in brain, spinal cord, and optic nerve. Mortality and anemia were not seen, but weight gain depression was detected in the inoculated elk over the 90 day experimental period.