A severe outbreak of toxoplasmosis was observed in a hare ranch (Lepus timidus ainu) in Sapporo. The data obtained are summarized as follows : 1. Outbreak occurred in rather warm season during the period of August 15〜September 11,1957. 2. Out of 13 hares including 8 adult and 5 about 1〜2 months old, total 8 had succumbed one after another within a short period. 3. Infection rate was higher in adult (7 out of 8-87.5%) than in young (1 out of 5-20%). No subclinical or latent infections were recognized clinically. 4. Disease runs a very acute course without representing any nervous symptoms. 5. Autopsy findings exhibited the necrotic changes completely in coincidence with those already reported. 6. Parasites were demonstrated heavily in the liver, spleen and mesenteric lymph node by the GIHMSA stained smear. The isolation of the parasites was successful in 1 case after 4 successive inoculations to mice. 7. The present observation in hare was the first reported in Japan
