The aim of the study was to determine leukocyte content in oral fluid of children with chronic catarrhal gingivitis (CCG) living in polluted areas with fluoride and iodine deficiency. The study comprised 120 children aged 7, 12 15 years residing in ecologically unfavorable areas of Lviv region and 80 children living in «conditionally clean» region were included as controls. CCG was diagnosed using the NF Danilevskiy classification (1994) in all surveyed. The level of leucocytes in oral liquid of 7-years-old children living in ecologically polluted region (EPR) was 1.4 times more than their peers from the conditionally clean region (CCR) 198.19±4.11)·106/l and (141.09±4.10)·106/l, correspondingly (p<0.01). In 12 years-old from EPR leukocytes number in oral fluid was 1.3 times higher than in children living in CCR ((246.81±4.16)·106/l against (190.02±4.11)·106/l, p<0.01 respectively). Further increase of leucocytes numbers was observed at the age of 15 in children of EPR (297.53±4.15)·106/l, which was 1.2 times higher than their peers, living in favorable environmental conditions (p<0.01). The age-dependent increase of leucocytes numbers in oral fluid is noted in children with CCG living in ecologically polluted region relatively to the data in children from conditionally «clean» region.