This study was undertaken to examine the performance of cleaning systems applied to food equipment. The contribution by the components of those systems to the performance of the total system was determined. A cleaning simulator was constructed in which test pieces in 4 test cells were subjected to 25 to 35 cycles, each of 12h. Each cycle the test pieces were: soiled for 45 min. in pasteurised milk (at 30°c) dosed with 10⁶ bacteria/ml of Streptococcus faecalis, Escherichia coli or Enterobacter aerogenes; serially treated with the rinses, detergents and sanitizers of the experimental cleaning system; and left for 9.5h intercycle (rest) period. The changes in the soil mass with time on stainless steel, rubber and glass test pieces were determined gravimetrically. The changes in the numbers of the dosed and non-dosed organisms on the surfaces, after components of the cleaning system had been applied, were determined by a swab-recovery/ plate-counting system. The surfaces were also examined by scanning electron microscopy. Four experiments were performed using this technique. A field experiment examined the performance of 5 cleaning systems over experimental periods of 5 weeks on 15 milking machines. The nature of the changes in the performance of the cleaning system over time were determined. Both detergents and sanitizers could, under varying conditions, contribute significantly to the bacteriological performance achieved by the system. A sanitizer applied for the complete intercycle period was more efficient than those applied for short contact-times. A post-wash sanitizer was slightly more efficient than a sanitizer applied before milking. The cycle of bacterial deposition onto the equipment surfaces, attachment, depletion by the cleaning system, growth during the intercycle period, and subsequent contamination of the milk at the next milking was studied. All three dose organisms attached actively, and were then largely removed by the cleaning system. Despite there being a large amount of soil on the surfaces of the test pieces, the intercycle conditions (30°c at up to 90% RH for 9.5h) were insufficient for growth. The effect of the amount of soil on the surface on the ability of bacteria to survive the application of a system or system component was examined. The minimum soil levels necessary for an organism to survive a treatment (Total Effect Maximum) and the minimum soil necessary for all organisms to survive a treatment (Zero Effect Minimum) were determined for systems and system components. The data was used to discuss the principles to be followed in designing a cleaning system. The principles were applied to the design of a system to clean a milking machine with cold solutions by soak techniques.