A chemical's ability to persist in the environment is an important criterion in determining whether concern is warranted.  Screening is commonly conducted based on the maximum degradation half-life of a chemical in any given medium or in terms of model-based estimates of a chemical's overall persistence in the environment.  In practice, however, both approaches are hindered by the limited availability of degradation half-life data.  Based on a trade-off between data requirements and error, guidelines are presented to help predetermine which half-lives are likely to be pertinent in both approaches.  The guidelines reduce the degradation data requirements by approximately 50% for the 318 chemicals addressed.  Using such guidelines to predetermine pertinent data in conjunction with steady-state multimedia models provides conservative estimates of overall persistence (no false negatives).  Preliminary screening based on the maximum degradation half-life predetermined to be pertinent using the guidelines is a more straightforward methodology but it is demonstrated that false-negatives (under-estimations), as well as an increased number of false-positives, are generated.