Open-system infra red gas analysis was used to measure the CO2 output throughout a year of four species of earthworm. The respiratory quotients (R.Q.s) of the four species were determined by means of a Warburg apparatus and it was found that they varied with season. In some instances R.Q.s did not fall within the expected range of 0.7 to 1.0 and the low values were attributed to calciferous gland activity and the fixation of metabolic CO2.The results from CO2 output measurements at 10°C and R.Q.s were used to calculate oxygen uptake, this varied seasonally but the mean annual values at 10°C for adult, large immature and small immature A. rosea were 64.17, 72.66 and 78.56 μl O2 g-1 fresh wt h-1 respectively. Mixed size groups of L. castaneus had a mean annual oxygen consumption at 10°C of 155.83 μl O2 g-1 fresh wt h-1 and equivalent values for D. rubida and O. cyaneum were 112.02 and 69.35 μl O2 g-1 fresh wt h-1. The apparent relationship between a high respiratory rate per unit weight and a litter dwelling habit (e.g. L. castaneus and D. rubida) disappeared when allowance was made for the weight of gut contents. Mean annual values for oxygen uptake in μl O2 g-1 gut free fresh wt h-1 at 10°C were L. castaneus (194.79), D. rubida (142.22), A. rosea (95.70) and O. cyaneum (139.28). No size specific metabolism could be demonstrated either within or between species, this is believed to be correlated with the different levels of activity shown by different species and their life stages.Rates of oxygen consumption per unit weight for A. rosea were shown to be proportional to ambient temperature. Q 10 slopes of this relation, between 6 and 15°C, were higher for large immature A. rosea (2.42) and small immatures (1.96) than for adult clitellate worms (1.42). The mean Q 10 relationship for all size classes of A. rosea was 1.93 over the same temperature range and the equivalent value for cocoons was 1.63. The relationship between the oxygen consumption rate of all size classes of A. rosea and ambient temperature was not significantly affected by acclimatisation at 5 and 10° C prior to measurements being made at 6, 10 and 15° C.