The chlorophyll conten and growth activity are gl eatest in the top parts of the thallus. A good logarithmic regression was found between the proportion of chlorophyll and the dry weight of the thallus, and a corresponding logarithmic regression was found between the rate of GO:! exchange (per gram dry wt.) and the dry weight. Good linear regressions were found between the net photosynthesis and the dry weight, and between the net photosynthesis and the chlorophyll content. 'Within the size classes studied there seems to be linear regression between the rate of CO:! exchange (per grn. dry wt.) and the proportion of chlorophyll. The ratio of chlorophyll a to chlorophyll b was found to be less than 2 in the top and more than 2 in the lower parts. There is a clearly defined active zone in the top of Cladonia alpestris. Therefore the suggestion is made that methods are to be developed for dividing the lichen biomass into different parts when making measurements on an areal basis. A further suggestion is that even the simple sampling procedure of taking 1 cm from the top of the thallus might give more easpy comparable material e.g. for chemical analyses