High titres of pertussis toxin (PT) antibody have been shown to be predictive of recent infection with Bordetella pertussis. The seroprevalence of standardized anti-PT antibody was determined in six Western European countries between 1994 and 1998 and related to historical surveillance and vaccine programme data. Standardized anti-PT titres were calculated for a series of whole-cell and acellular pertussis vaccine trials. For the serological surveys, high-titre sera (> 125 units/ml) were distributed throughout all age groups in both high- (> 90%) and low-coverage (< 90%) countries. High-titre sera were more likely in infants in countries using high-titre-producing vaccines in their primary programme (Italy, 11.5%; Western Germany, 13.3%; France, 4.3%; Eastern Germany, 4.0%) compared to other countries (The Netherlands, 0.5%; Finland, 0%). Recent infection was significantly more likely in adolescents (10-19 years old) and adults in high-coverage countries (Finland, The Netherlands, France, East Germany), whereas infection was more likely in children (3-9 years old) than adolescents in low-coverage (< 90%; Italy, West Germany, United Kingdom) countries. The impact and role of programmatic changes introduced after these surveys aimed at protecting infants from severe disease by accelerating the primary schedule or vaccinating older children and adolescents with booster doses can be evaluated with this approach. (Résumé PubMed)