Gravity separation has been used for traditional cheese making of Grana Padano and Parmigiano-Reggiano cheeses. This process allows the whole milk to be standardized to a 2.2% fat. Traditional cheese makers have stated that they continue to use gravity separation as opposed to more modern centrifugal separation due to the difference in quality and flavor of cheese. Our first objective was to determine if immunoglobulins (Ig) play a role in the gravity separation (rising to the top) of somatic cells (SC) in skim milk. Other researchers have shown that gravity separation of milk fat globules is enhanced by IgM. Our recent research found that bacteria and SC gravity separate in both raw whole and skim milk and that heating milk to >76.9oC for 25s stopped gravity separation of milk fat, SC, and bacteria. Bovine colostrum is a good natural source of Ig. An experiment was designed where skim milk was heated at high temperatures (76°C for 7 min) to stop the gravity separation of SC and then colostrum was added back to try to restore the gravity separation of SC in increasing increments to achieve 0, 0.4, 0.8, 2.0, and 4.0 g/L of added Ig. The milk was allowed to gravity separate for 22 h at 4°C. The heat treatment (76°C for 7 min) of skim milk was sufficient to stop the gravity separation of SC. The treatment of 4.0 g/L of added Ig was successful in restoring the gravity separation of SC as compared to raw skim. Preliminary spore data on the third replicate suggested that bacterial spores gravity separate the same way as the SC in raw, and heated skim with 4.0 g/L of added Ig. There is strong evidence that Ig are at least one of the factors necessary for the gravity separation of SC and bacterial spores. Our second objective was to determine the role that Ig and somatic cells (SC) play in the gravity separation of milk. There were 9 treatments: (1) low temperature pasteurized ( LTP) (72°C for 17.31s) whole milk, (2) LTP (72°C for 17.31s) whole milk with added bacteria and spores, (3) recombined LTP (72°C for 17.31s) whole milk with added bacteria and spores, (4) high temperature pasteurized (HTP) (76°C for 7 min) whole milk with added bacteria and spores, (5) HTP (76°C for 7 min) whole milk with added bacteria and spores and added colostrum, (6) HTP (76°C for 7 min) centrifugal separated gravity separated (CS GS) skim milk with HTP (76°C for 7 min) low SC cream with added bacteria and spores, (7) HTP (76°C for 7 min) CS GS skim milk with HTP (76°C for 7 min) high SC cream with added bacteria and spores, (8) HTP (76°C for 7 min) CS GS skim milk with HTP (76°C for 7 min) low SC cream with added bacteria and spores and added colostrum, and (9) HTP (76°C for 7 min) CS GS skim milk with HTP (76°C for 7 min) high SC cream with added bacteria and spores and added colostrum. The milks in 9 treatments were gravity separated at 4°C for 23 h in glass columns. The presence of both SC and Ig were necessary for normal gravity separation (i.e., rising to the top) of fat, bacteria, and spores in whole milk. The presence of Ig alone without SC was not sufficient to cause bacteria, fat and spores to rise to the top without SC. The SC may provide the buoyancy required for the aggregates to rise to the top due to gas within the SC. More research is needed to understand the mechanism of the gravity separation process. ii