We investigated two of the most studied relationships in the macroecological research program (species richness vs. body size and abundance vs. body size) of a local chironomid assemblage from southeastern Brazil. Although numerous studies have examined these relationships, few have investigated how they vary at different temporal scales. We used data from a forested stream to document and examine these patterns at monthly intervals. Both the species body size distribution and the abundance-body size relationship varied temporally. In some months the body size distribution was skewed to the right, whereas in others it approached normality. We found both linear relationships (with different values of slopes), and a polygonal pattern in the abundance-body size relationship. This temporal variation was not related to environmental variables. Our results suggest that body size relationships are temporally instable properties of this chironomid assemblage.