Purified sporulated oocysts of Eimeria maxima, isolated from chickens in Taiwan, were broken in a tissue grinder. The released sporocysts were treated with excysting fluid, consisting of 0.5% typsin and 5% chicken bile in PBS, to dissolve the Stieda body of the sporocyst and to initiate the sporozoite mobility. The excystation process of the sporozoite was examined under the light microscope. The sporozoite body may be constricted to about a quarter of its normal diameter as it pass through the gap in the sporocyst wall. The sporozite gradually protrded from the sporocyst in interval steps.