Oocysts of Eimeria angusta were recovered from the cecum of a captive ruffed grouse which died of coccidial typhlitis. Five experimental passages were made in grouse over a 2-yr period. Prepatent period was 6.5–7.0 days; sporulation time at 22 C was 54–60 hr. Endogenous stages were not found in grouse killed 1 and 2 days after inoculation (DAI). A few immature schizonts were in cecal epithelium 4 DAI. Developing and mature schizonts, and undifferentiated gamonts were in cecal epithelium 5 DAI. Developing micro- and macrogamonts, but no oocysts, were present 6.5 DAI. Fibrinohemorrhagic typhlitis, associated with large numbers of gamonts and oocysts in the epithelium, was found 9 DAI. Cecal glands were hypertrophic and there was a heavy mixed inflammatory cell reaction. Diarrhea, depression and reduced feed intake occurred 7–10 DAI with most severe signs and greatest oocyst passage 8 or 9 DAI. Most infected birds lost weight 5–8 or 9 DAI, but none died.