In the dynamics of the survival of chromosomal polymorphism selection may be operating at the genic level, at the chromosomal level or at the supergene level. Tests designed to distinguish between these levels were run on Drosophila pseudoobscura. There was no evidence for heterosis, a necessary requirement for gene-determined chromosomal polymorphism A strong chromosmal selection was observed. No evidence was found for the presence within one locality of more than a single superallele for each supergene (equals gene order). These results are compared to those found by others.