This study was undertaken to determine the loss in milk-production of each quarter of the udder in which bacterial infection was present and also to ascertain its influence on certain milk components. Milk analyses were done on milk samples from 432 individual quarters. The following parameters were determined; cell count as well as sodium-, potassium-, lactose-, protein- and fat concentrations in the milk. It was found that infected quarters produced 37% less milk than equivalent normal quarters. It was also established that the total cell count of infected milk was much higher than the cell count of milk from equivalent normal quarters. When the cell count from infected quarters were converted to a percentage, based on those of normal quarters, the average increase was 1079%. Bacterial infection of a quarter inhibited the average concentration of potassium and lactose with 16,7% and 12,1%while the sodium concentration increased by 86,4%. Bacterial infection had no significant influence on fat and protein concentration.