Data have been gathered and collated from a variety of sources both published and unpublished, dealing with the concentration of enteroviruses in human stools. For polioviruses, a general range of 3.0-6.5 log10 TCD50 per gram of stool was reported, whereas for coxsackieviruses and echoviruses the range has been from 2.0-5.5 log10 TCD50. As human stools average about 100 gm, it is not unusual for an infected person to excrete as much as 10-300 million TCD50 of virus daily. The results of enterovirus titrations are significantly affected by the types of cultures in which the tests are conducted. With certain kinds of cultures (eg, human kidney for polioviruses), comparative tests showed titers to be at least one log unit higher per gram of stoll than the titers of the same strains titrated in monkey kidney cultures. Since almost all of the titrations included in this report were carried out in monkey kidney cultures, the concentration of virus in many cases may be assumed to be ten times higher than that reported. Some of the data collected also contributed information on the duration of enterovirus excretion. These data reemphasize the fact that a person in the course of an asymptomatic enterovirus infection may excrete the virus over a period of many weeks, with about 50% of those infected continuing to shed virus into the third and fourth weeks of infection.