A high-speed supernatant extract was obtained from infective oocysts of Eimeria tenella homogenised in a sucrose-low ionic strength buffer. Immunoblotting showed this soluble, micropore-filtered preparation (designated E1) to be rich in actin. E1 underwent superprecipitation on addition of ATP but not its non-hydrolysable analogue AMP.PMP--behaviour typical of an actomyosin solution. The superprecipitate fluoresced strongly in the presence of rhodamine-phalloidin (indicative of the presence of F-actin) and electron microscopy of negatively-stained preparations of this flocculent matter confirmed the abundance of filamentous material within it. This is the first demonstration of a functional actomyosin isolated from a member of the economically important phylum Apicomplexa.