Natural defenses are mobilized in response to bacterial contamination of the uterine lumen after calving. A significant influx of leukocytes takes place in the endometrium, and subsequent reproductive performance of the cow may be impaired if endometritis persist beyond 21 days. A reliable diagnostic technique is needed to evaluate the condition of the uterus after calving. The objective is to identify diseased animals and to avoid treating females with antibiotics that do not need treatment. An examination of vaginal secretions appears as the most reliable technique to be used. It should be given preference over transrectal palpation or ultrasonography of the uterus which tend to overestimate the number of diseased animals. We recommend as a routine procedure, the examination of vaginal secretions approximately one month after calving.