The use of cleaned-in-place milk pipe lines has been increasing for the past several years, particularly in conjunction with the farm bulk tank. It offers an opportunity for increasing operating efficiency by reducing the amount of labor needed for the milking operations. For many dairymen who have either outgrown or worn out existing facilities it is the least expensive and most efficient way of improving their milk handling facilities. The use of pressure in circulation cleaning of permanent milk pipe lines has been developed to give satisfactory results in the dairy plant. This method involves the use of considerable extra equipment which may be used for other purposes. Pipe line milker installations on most dairy farms are cleaned by the use of vacuum circulation rather than by pressure circulation cleaning. This enables the dairy farmer to utilize the same vacuum pump for circulation cleaning of the pipe line that is used for the milking operation. This eliminates the purchase of extra equipment that would be of no value except in the cleaning operation. Our present knowledge of the factors involved in the installation, the maintenance, and the care of cleaned-in-place milk pipe lines on the farm is limited. Dairymen who are now using such a system, and those considering its use, need more scientific information on the cleaning and sanitizing aspects of the farm milk pipe line installations. Cleaning compounds which have been designed for hand cleaning operations are commonly used for pipe line cleaning. It is impossible to obtain maximum cleaning efficiency of pipe lines with these compounds because they are milder in their alkaline action than compounds designed for in-place cleaning. The chemical activity of compounds designed for in-place cleaning is increased by the maintenance of a temperature of 140 °F. or higher. The circulation temperature range of 140 to 160 °F. as recommended by the several detergent manufacturers is difficult to maintain in actual practice. Many detergents recommended for circulation cleaning are not suitable for use in all types of farm-in-place installations due to the excessive foaming of the detergents in solution when placed under vacuum. This excessive foaming causes considerable difficulty in circulation operations and prevents proper solution contact with the pipe line surface. The problem of cleaning and sanitizing cleaned-in-place pipe lines on dairy farms is confounded by the absence of standardization in the engineering aspects of cleaned-in-place systems. The introduction of shortcuts or laxity in following the proper cleaning and sanitizing procedures may result in the lowering of milk quality. The primary objective of this investigation was to evaluate the cleaning and sanitizing ability of a number of cleaning compounds used in the vacuum circulation cleaning of a pipe line milker in a stanchion type dairy barn. A second objective was to evaluate the effect of circulation temperature ranges on the cleaning efficiency of the detergents. / Master of Science