On the basis of a two-weekly sampling programme throughout a year, biomass dynamics and energy budgets were estimated for two forest floor Collembola, Orchesella cincta (L.) and Tomocerus minor (Lubbock) in a pine forest plantation in the Netherlands. The two species together made up 40 % of the total Collembola density and 70% of its biomass. The density of both species fluctuated greatly throughout the year, but their standing crop demonstrated only moderate changes. Biomass losses to mortality were greatest in autumn; production changed synchronously with mortality. Biomass turnover (P/B) was higher for O. cincta (8.3 yr -1 ) than for T. minor (6.7 yr -1 ). Both estimates are somewhat lower than those predicted on the basis of an allometric relation with body-size, but are considerably higher than those reported for other (soil living) Collembola species. A relation between biomass turnover and position in the soil profile is suggested to explain this discrepancy. Biomass turnover of cuedaphic species may be lower because the soil acts as a refuge from predation and permits a lower production, compared to the above ground fauna. The total consumption of the Collembola community was estimated as 600 kJ m -2 yr -1 , which is equivalent to about 6% of the annual leaf litter fall. On the basis of the present data, the role of Collembola in the energy metabolism of soil communities may be greater than thought hitherto.