The effect of rinsing and washing with chlorinated alkaline detergents on the protein and fat present in milk soils was studied as a function of temperature, time and length of milk contact before cleaning. Milk containing either I131-labelled protein or I131-labelled fat was recirculated through a test chamber for varying times, after which the chamber was rinsed with water then washed with a detergent solution. Soil removal was monitored by measuring radiation in the test cell during the cleaning procedures. Fat and protein studies yielded similar results showing rapid soil removal at the beginning of water rinses and hot detergent washes tapering off after 1 to 2 min to very little additional soil removal. The rinse water temperature does not greatly affect soil removal, but conventional chlorinated alkaline detergents perform very poorly at 20°C and show a much more linear rate of soil removal at this temperature. Soil deposition increases with milk contact time as does the fat portion of the soil which is always at least four times greater than the protein. Results are consistent with the soil immediately adjacent to the contact surface being primarily milk protein and the outer soil being mostly milk fat.