Thirty red-legged partridges (Alectoris rufa), 5-month-old, were orally inoculated with oocysts of the OV-51/95 strain of Toxoplasma gondii. Birds were distributed into five groups and received, respectively, 10 (group A, 4 birds), 50 (group B, 14 birds), 10(2) (group C, 4 birds), 10(3) (group D, 4 birds) and 10(4) (group E, 4 birds) oocysts. One partridge from group B and one from group E died suddenly of acute toxoplasmosis at 7 day after inoculation (DAI) with demonstrable T. gondii in several tissues. The rest of birds remained clinically normal until killed at 44, 58, 65, 72, 79 or 100 DAI. Brain, heart, liver and skeletal muscle from these partridges were bioassayed individually in mice; T. gondii was demonstrated in all these tissues, except in heart of three birds inoculated, respectively, with 10, 50 and 10(2) oocysts. Lesions were not seen in histologic sections of tissues from surviving partridges. These results suggest that red-legged partridges are resistant to clinical toxoplasmosis.