The population of Flix (region of Ribera del Ebro, Tarragona) is highly exposed to hexachlorobenzene (HCB) due to the closeness of an electrochemical factory. Although the degree of HCB contamination in this population is still high, concentrations of HCB in the sera of women aged 18-40 years from 1997 to 1999 were 61% lower than those observed in 1994 (4.1 ng/ml vs. 10.6 ng/ml). Concentrations of dichlorodiphenyl dichloroethane (p,p'-DDE) and beta-hexachlorocyclohexane (beta-HCH) also decreased, although the difference was not statistically significant. In contrast, concentrations of polychlorinated biphenyls (PCB) in the period 1997-1999 showed a nonsignificant increase compared with those in 1994.