Oxygen budget studies on meiofauna from a Northern Ireland beach indicated that respiration was lowest when the ambient temperature was 12ºC and that oxygen uptake rates were affected by the test organism batch-size. Further work has shown that the gastrotrich Turbanella varians acclimated from 8 ºC has lower respiration at 12 ºC than at 8, 10, 14 or 16 ºC. Respiration increases substantially after 24 h in sterile seawater at all the temperatures tested. Experiments show this is probably due to food searching activity. It is shown that oxygen uptake per individual in the gastrotrich Neodasys chaetonotoideus declines with population density in the sample test chamber. This is due to a substance produced by Neodasys itself and is a further example of chemical organization amongst meiofauna. Additional parameters such as ambient temperature and population density must be taken into account if laboratory data are to be effectively extrapolated to field situations.