Previous studies on the Moor House Enchytraeidae by Peachey (1959, 1963) and Springett (1962, 1967) give the distribution and density of many species from various sites on the reserve together with information on life histories and life cycles. It appears that, on the Calluneto-Eriophoretum blanket bog which covers most of the reserve, Cognettia sphagnetorum (Vejdovsky) is the dominant enchytraeid and it was, therefore, decided to concentrate on this species and to rely on existing population data for the four other species to be found in small numbers on the blanket bog sites. The first object was to determine the population structure of C. sphagnetorum, to estimate mortality and annual production. The species reproduces asexually by fragmentation, like Enchytraeusfragmentosus Bell (Bell 1959). This part of the work was based on field samples taken between April 1968 and March 1970 and on laboratory cultures to study growth, fragmentation and regeneration. The data were then used in a mathematical model to estimate mortality and field production. At the same time experiments, using a Cartesian Diver respirometer, measured the rates of oxygen consumption by Cognettia sphagnetorum. Nielsen (1961) and O'Connor (1963) had already measured respiration of Enchytraeidae and estimated field population respiration (including a small species of Cognettia) but further experiments were necessary in view of the low temperatures at Moor House and the lack of information on the effect of acclimatization.