An important cause of infertility in dairy cattle is uterine contamination, infection and inflammation that occur at the time of calving and persist until the time when the cow should be bred. Most cows have some post-partum uterine contamination and, under normal circumstances, the natural resistance of the uterus eliminates the contamination and inflammation and the uterus recovers. However, if infection remains, it is a cause of inflammation and infertility. The standard treatment for uterine infection is infusion of antibiotics into the uterus. This treatment is widely used in California. The purpose of this research was to determine the incidence of this condition and determine the efficacy of the treatment. In addition, observations were made on the identity of the bacterial contaminants of the uterus, their susceptibility to commonly used antibiotics and the absorption and excretion of antibiotics, including determination of antibiotic residues in milk following infusion.