Thirty battery-hatched chukar partridges (Alectorts graeca) were inoculated orally with oocysts of the ME 49 or the GT-1 strain of Toxoplasma gondii. All six chukars given 10,000 GT-1 strain oocysts died or were euthanized between postinoculation day (p.i.d.) 3 and 6. Fifteen of 24 chukars given 10,000, 1000, 100 or 10 ME 49 strain oocysts died or were euthanized between p.i.d. 6 and 14. Nine chukars that were not ill by p.i.d. 14 remained clinically normal until euthanized in good health p.i.d. 47 and 67; T. gondii was found by bioassay in mice inoculated with tissues of these nine chukars. From the tissues of five chukars bioassayed individually in mice, T. gondii was isolated from brains of four of four tested, and from the hearts and skeletal muscles of five, and livers of three of five chukars tested. Major lesions in chukars that died or those euthanized when ill were enteritis, splenic necrosis, myocarditis and encephalitis. Myocarditis and encephalitis persisted in chukars examined p.i.d. 47, 53 and 67. All chukars examined p.i.d. 10 developed anti-T. gondii antibodies. Anti-T. gondii antibodies detected in the modified agglutination test were higher than those in latex and haemagglutination tests. The Sabin-Feld-man dye test did not detect T. gondii antibodies in sera of chukars. The ME 49 strain of T.gondii was more pathogenic to chukars weighing >/= 300 g than to the 25 g Swiss Webster mice.