The smoking habits in 287 Norwegian soldiers, mean age 24 years, who served for six months in the United Nations' peace-keeping forces in Lebanon was studied by self-administered questionnaire and determination of serum-thiocyanate. According to the questionnaires and verified by serum thiocyanate 42% were non-smokers at departure, 88% of them were still non-smokers at return. 7% of the smokers quit smoking while in Lebanon. The other smokers increased the consumption of cigarettes. The study indicates that campaigns against smoking should preferably be directed toward the youngsters since success among them will have long lasting effect.