No systematic review is available on studies conducted in Spain on human concentrations of persistent toxic substances (PTS). The objectives were: to identify studies conducted in Spain in the past 30 years that determined concentrations in humans of dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDE), hexachlorobenzene (HCB), hexachlorocyclohexane (HCH) and polychlorinated biphenyls (PCBs); and to summarize the main characteristics and results of each study. Studies are highly heterogeneous and most lack population representativeness. Concentrations of DDT and DDE might have decreased moderately in the last 20 years. Numerous fluctuations are apparent in levels of HCB, HCHs and PCBs, in some instances compatible with some stagnation. There are enormous differences in levels detected across and within studies: PTS concentrations of some individuals may be over 200-fold higher than those of others. The actual magnitude of human contamination by PTS and their trends across Spain -as well as the geographic and social heterogeneity- remain largely unknown.