In Spain, there are substantial gaps in available information about contamination of food, humans, and the environment by persistent toxic substances (PTSs), although studies have shown detectable concentrations of DDE, PCBs, hexachlorobenzene, or hexachlorocyclohexane in 80-100% of the population. Spain will soon try to implement the Stockholm treaty on persistent organic pollutants (POPs). A country that ratifies the treaty is required to develop a National Implementation Plan (NIP). Such NIPs should provide for studies of factors that influence body concentrations of PTSs in the population, and thus ultimately reduce PTS data gaps. Spain's PTS-related problems are similar to those of many other countries. Elucidation of their causes, consequences, and possible solutions will be of benefit beyond national boundaries.