The potential preventability of serious helicobacter-associated diseases - especially gastric cancer - has evoked interest in eradicating this pathogen from the population. We assessed the efficacy of the pioneering screen and treat intervention project in Vammala by studying helicobacter seroprevalence in pregnant women representing the normal population. Consecutive maternity clinic samples from native Finnish females at five different localities in 1995 (n=701) and 2000 (n=772) were investigated for class IgG H. pylori antibodies by enzyme immunoassay (Pyloriset EIA-G III, Orion Diagnostica, Espoo, Finland). In Vammala the change in helicobacter seroprevalence was -13%-units (between 1995 and 2000; p=0.0125, chi-square test) in > or =29-year-old females, +1.6%-units (difference statistically non-significant) in <29-year-old females, and -5.5%-units (difference statistically non-significant) in the whole study population. In the four reference localities studied, all the corresponding changes remained statistically non-significant. Thus, in Vammala the programme applied accelerated the decline of helicobacter infections in 29- to 45-year-old females and in 2000 the seroprevalence rate had also become significantly lower than that of the four reference communities combined (7.6% versus 13.5%, respectively, p=0.0433, chi-square test). The final outcome of the intervention project, i.e. the long-term effect of this decline on gastric cancer and peptic ulcer disease, remains to be evaluated.