The pathology and pathogenesis of blackquarter was elucidated in guinea pigs by intramuscular inoculation of spores/culture/toxin of Clostridium chauvoei strain 49. Characteristic symptoms of blackleg were produced. Haemoconcentrations, decreased platelet and leukocyte counts, neutrophilia, glucose values between 112 and 145 mg/dl, and presence of sugar and protein in urine were recorded. Grossly the hair on skin at inoculated site were sparse and easily depilated. Subcutaneous tissue was oedematous with gelatinization of fat. Muscles were blackish-grey, hyalinized, necrosed and infiltrated with fibrino-haemorrhagic exudate and neutrophils.