This study investigated rate of contamination in simulated in-use intravenous solutions to obtain data from which to recommend a standard time period for the administration of intravenous solutions. Although the Center for Disease Control and many medical institutions have recommended that all bottles of in-use intravenous solutions be changed every 24 hours, there are no published data to support the 24-hour standard. In this study, samples were drawn from 80 bottles of Ringer's Lactale solution at predetermined time intervals over 48 hours and cultured on blood agar plates to determine rate of contamination. A low incidence of intravenous solution contamination was found at all time periods. Of 430 total samples, only 12 (2.8 percent) were contaminated. Results of this study did not indicate a significant relationship between time and contamination of simulated in-use intravenous solutions. Therefore, contamination that does occur within 48 hours in intravenous solutions must be introduced from some exogenous source. Further research is required to elucidate exogenous sources of contamination. In the meantime, it can be concluded, the 24-hour standard is adequate to protect against contamination that would occur solely from preparation of the intravenous solution for administration.