The organisms recovered from the uterus after labor in the majority of cases of "puerperal pyrexia" are similar to those in normal puerperia. It seems possible that injuries are the chief factors determining the minor patho-genicity of which they appear to be capable on occasion. Streptococcus pyogenes is occasionally found in the absence of symptoms of disease, but in that case it is always in association with other organisms. When S. pyogenes is found in cases of "puerperal pyrexia" the severity of the illness is proportionate to the number of streptococci. The presence of S. pyogenes in the cervix uteri should remove the case from the category of "puerperal pyrexia" and allot it to that of "puerperal fever." A means of differentiating S. pyogenes infection from others is required in cases of doubt and in every case occurring during an outbreak of puerperal sepsis. Bacteriological examination of the cervix uteri is an effective method of diagnosis. The uterus is rapidly invaded by bacteria from contiguous surfaces early in the puerperium. Uterine infection normally increases up to the 3rd or 5th day and afterwards diminishes.