Introduction:
Knowledge of the harmful influence of environmental tobacco smoke (ETS) has a positive impact on changing social behaviours worldwide. In many homes smoking is totally prohibited; in some others, partial limitations of tobacco consumption have been introduced.

Objective:
To study the correlation between the adopted rules of tobacco use in homes of 3-year-olds, and the kind and frequency of acute respiratory system infections within a 6-month period of attending pre-schools.

Material and Methods:
The study was performed among children attending municipal pre-schools in Białystok, Poland. The data was collected by anonymous questionnaires completed by the parents of 302 children aged 3 years chosen randomly from 1,200 children attending 51 pre-schools. The exposure of children to tobacco smoke was measured by determining cotinine to creatinine ratio (CCR) in urine.

Results:
In the 150 families of children who were surveyed, 210 were smokers. Every day, the smokers consisted of fathers (37.3%) and mothers (23.6%). The 3-year-old children were divided into 3 groups according to smoking habits in their homes: 28.5% of the children under examination came from homes where tobacco smoking was forbidden (mean CCR – 15.21ng/mg, SD=11.86), 26.2% came from homes where tobacco was smoked in separate rooms (mean CCR – 65.75 ng/ml, SD=81.51), 45.4% lived in homes where no rules connected with smoking had been established (mean CCR – 61.75 ng/ml, SD= 70.29). During the analyzed period of 6 months, 85% of the children had at least 1 respiratory tract infection (60% – upper, 16.9% – lower, 16.5% – upper and lower, 7.1% – otitis media).

Conclusions:
The majority of the 3-year-old children who had lower respiratory tract infections required antibiotics and hospitalization. Living in a home where no tobacco rules were established may cause an increase of respiratory tract infections.