Sporocysts from the goshawk (Accipiter gentilis) were experimentally transferred to the mouse (Mus musculus). It was found that the goshawk is the host of one of the sarcosporidians inducing muscle sarcocystosis in mice. Thin-walled, sporulated oocysts expelled by the goshawk measured 16.5-19.0 X 12.0-13.0 micron. Those which measured 12.0-13.5 X 8.2-9.0 micron were widely elliptical, with rounded poles. No asexual reproduction of parasites was detected in the viscera of mice. The cysts started to appear in skeletal muscles on day 20 after oral infection with 10,000 or 100,000 sporocysts per mouse. The cysts measuring 15-630 X 18-65 micron contained widely oval metrocytes (2.8-4.3 X 1.5-2.8 micron) or banana-shaped cystozoites (6.0-8.0 X 2.0-3.8 micron). Three months after infection the cysts were found also in the tongue of mice. No morphological differences were observed between the oocysts-sporocysts from owls (Tyto alba and Asio otus) and goshawk, not even between the muscle cysts of these sarcosporidians in mice. The possibility of passaging the species Sarcocystis dispersa from the long-eared owl through the digestive tract of goshawk is discussed.