The effect of habitat conditions on the size and number of phycobiont cells, on the con tent of chlorophylls and carotenoids in the thalli of Cetraria islandica, Cladina arbuscula, Hypogym- nia physodes, Parmelia sulcata and Peltigera rufescens were investigated. Seasonal differences were found in the size of phycobiont cells. The mean size of algal cells increases from February to Octo ber, the smallest were observed in the winter. Lichen species collected from the sites distant from town were characterised by the largest number of phycobiont cells and the highest percentage of live cells, hence the high content of photosynthetic pigments. Seasonal differences were observed in chlorophyll content in lichen thalli. The highest pigment concentration was found in thalli collected in the winter and spring, the lowest were noted in the summer. lichen thalli, phycobionts, photobionts, photosynthesis pigments