AbstractPrevious attempts at structure/biodegradability relations (SBRs) and available biodegradation data are reviewed and it is concluded that (1) not enough rate data on large numbers of chemicals are available to develop quantitative SBRs and (2) attempted qualitative SBRs have suffered from either poor documentation of the biodegradation evaluation or they have used limited biodegradation test data. Because of the poor reproducibility of biodegradation tests, a weight‐of‐evidence evaluation procedure is proposed. A system for collecting and evaluating biodegradation data from screening tests, biological treatment simulations, grab sample tests and field studies is described and study‐specific and summary biodegradability codes in combination with reliability codes are developed that can be used for structure/biodegradability rela