Technical Abstract: Automated systems to record milk weights of individual cows at each milking are now common on dairy farms. These data are used by DHIA for testing purposes and by farmers to monitor herd performance. Despite the importance of these data, little effort has been made to monitor the function and reliability of milking stalls and recording equipment on a daily basis. Described is an algorithm which allows continuous monitoring of the function of individual milking stalls. The basis the algorithm is the comparison of milk production of individual cows over a period of days. For each cow, milk production at a selected stall is compared to production of that same cow when milked at any other stall. These ratios are averaged across all cows milked at least once in the selected stall and once at any other stall. Ideally, the average ratio for each stall should be 1. Stalls where the average ratio deviates from 1 by more than 5% are assumed to be malfunctioning. This algorithm was implemented as a computer program and was used to identify 3 malfunctioning stalls out of 12 at the USDA dairy facility at Beltsville, MD. The algorithm can easily be incorporated into existing management programs or used as a separate program. In either case, routine use of this algorithm can improve the reliability of DHIA test programs and potentially reduce the incidence of new mastitis infections by detecting malfunctioning milking equipment.