Eimeria dispersa was isolated from young, intensively housed turkeys in Britain. The parasite has morphological features in common with those of the original description. At least two generations of schizonts occur before gametogony and one or two more schizont generations are concurrent with gametogony. Four generations of schizonts are needed to account for the observed reproduction index of 2.08 x 10(6)/oocyst inoculated. The first oocysts were discharged by 105 h and these sporulated within 30 h at 30 degree C. A single dose of between 1 x 10(2) and 1 x 10(6) oocysts depressed body weight gain of 3-week-old poults and 2 poults died 6 and 12 days after receiving 1 x 10(4) or 1 x 10(6) oocysts. A single dose of oocysts protected against a challenge inoculation given 14 days later. Poults immunized against E. dispersa were resistant to challenge with a strain of E. dispera obtained from the United States. Electrophoretic examination of 2 enzymes from both strains of E. dispersa showed that they had similar mobilities. Attempts to infect chickens, guinea-fowl and Japanese quail with E. dispersa were unsuccessful. The strain of E. dispersa isolated here is best referred to as E. dispersa (Briston).