When periphytic organisms growing on artificial plants were grouped in logarithmically increasing size classes, patterns in the distribution of biomass were consistent over the season and under different grazing regimes, despite taxonornical changes in the dominant taxa of algae and invertebrates. The amount in each size class was not constant, and instead, certain classes tended to have values consistently lower or higher than the mean. The locations of these peaks and troughs in the size distributions coincided with those observed in lake plankton. Despite these irregularities, the hypothesis that the biomass in logarithmic size classes is constant apparently applies at a crude level, for the biomass of most size classes lay within an order of magnitude of the mean. This rule of thumb also applies to the littoral fish community, for the minnow biomass was approximately that in a periphyton size class.