We studied tuberculin reactivity in young Norwegian adults and its possible dependency on age, gender, previous BCG vaccination, smoking habits, occupational exposure, diet as well as years of education as a measure of socio-economic status. Responders of a random sample of men and women aged 20-44 years living in Bergen, Norway were interviewed and tested withthe adrenaline-Pirquettest with Norwegian-produced synthetic mediumtuberculin at the out-patient chest clinic in the city of Bergen in 1992-1993. Nine hundred and three subjects out of 1200 met for the clinical examination (75%). Five hundred and eighty-eight subjects were tuberculin-tested and read, whereof 95% were BCG vaccinated by age 14. Mean tuberculin reactivity was 4.8 mm (SD: 3.0 mm). A positive reaction (> or = 4 mm) was found in 64%, whereof 7% had a strongly positive reaction (>10 mm). A negative reaction (