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Relationships between individual organism size and abundance from picoplankton to mesozooplankton are examined in the planktonic community of an oligotrophic, high mountain lake. The overall, time-integrated biomass spectrum shows a slope very close to zero. In addition, the presence of a discontinuity within the size range and the clear tendencies in the distribution of the residuals make the definition of an allometnc model on this scale difficult. At the smaller scale of subgroups (pico-, nano-, micro- and mesoplankton) there is a clear increase of biomass per unit water volume with body size. Our results suggest that, at least in this small ecosystem, the ecological and evolutionary relationships which operate at the secondary scale are more important in structuring the community than the physiological factors (size-dependent metabolism) which determine the primary scaling.