The total (a + /?) carotene and the chlorophyll a content of fresh water phytoplancton were measured spectrophotometrically and were found to be higher during autumn and a part of the winter (100 to 200 ng/l chlorophyll a and 4 to 6 /rg/1 total (a and [!) carotene) with maxima during December and January. From March to June the content decreased continuously from 50 fig to 20 ng (or even 10 /rg/1) chlorophyll a and from 5 /rg to less than 1 jug/l total carotene (a + [!). The ratio of the a-carotene to the content, fluctuated periodically. During January to May more a-carotene than /i-carotene was found and during the rest of the sampling period more /J- than a-carotene.