Species-specific antisera were used in agar-gel precipitin reactions to determine the presence of serum proteins from pig, horse and rabbit flesh in saline extracts of fresh ground beef that contained flesh from these species. Precipitin lines of identity were observed between species I serum and extracts obtained from ground beef which contained 1, 3 and 5% species flesh. No reactions were observed with control bovine serum. The results indicated that serum albumin was the major protein detected for each species. This method could be used for the qualitative detection of species adulterants in fresh ground beef.