ŠTEFANEC M. 2019. Stomatal density of spruce (Picea abies L.): differences between years and altitude. Bachelor thesis, Zvolen: Technical University in Zvolen. Faculty of Forestry. 2019. 39 pp.The regulation of CO2 flow and water vapour flow between plant and air are often mentioned in connection with stomata. However, stomata are the gate for the income of atmospheric ozone into assimilatory organs too, especially in high-elevation forests. The research of stomata is therefore interesting in more aspects. We expected that measuring of stomata will reveal differences between a particular annual set of needles and between spruce (Picea abies L.) trees growing in different altitudes. The length of stomata is obviously connected to the overall number of stomata too. Hence, we assessed also this parameter in order to confirm the assumption that it will also be affected by climate in different altitudes or by weather during particular years. I measured needles of spruce growing in elevation of 1100, 1300 and 1500 m a.s.l. using scans. I measured needles from unshaded part of the crown of ten trees for each elevation, three needles were assessed for each of three annual sets. The ImageJ software was used to measure the length of each needle and stomatal density was assessed for 5 mm long segment. There was a significant effect of the year set on the length of needles. We found out significant differences between groups of trees from different altitudes in stomatal density. There was an inconsistent character of differences in year sets when compared between plots. Climatic data will be evaluated in future in order to explain revealed differences.