The compound-autosome technique is being used as a measure of intraspecific competitive ability in Drosophila. We will examine a series of inbred and outcrossed strains of Drosophila with respect to three, potentially very different, measures of population fitness: (1) intraspecific competitive ability (assayed by means of the compound-autosome technique), (2) interspecific competitive ability (assayed by competition with related species), and (3) equilibrium biomass. The objective of the research is to determine the correlation, if any, between these distinct measures of population fitness.