In the last few years, data have been rapidly accumulating on the more than 600 species of Hawaiian Drosophilidae (for review, see Carson et al., 1970). This fauna is notable not only for its size and the morphological complexity of its species but also for unusual behavioral characteristics. An extensive mass of data is also available on the ecology of these forms (Heed, 1968). That such remarkable evolution should have occurred within certain restricted terrestrial areas of these small oceanic islands presents many challenges to the population geneticist. Whereas genetic attention so far has been primarily concerned with phylogeny and the interisland founder effect (e.g. Carson and Stalker, 1968, 1969) crucial information on the dynamics of evolution in this group must necessarily come from studies of population structure and variability within individual species. The present paper is a preliminary report on intraspecific chromosomal polymorphism in three species endemic to the central Hawaiian islands of Maui, Molokai and Lanai. Because these three islands have been joined and separated at least twice during recent geologic time (Stearns, 1966) it is convenient to refer to them as the Maui complex (Fig. 1). The three species concerned, D. bostrycha, D. disjuncta and D. grimshawi all belong to the D. grimshawi subgroup (Carson and Stalker, 1968a). Except for the polymorphic inversions, all three species are homosequential, that is, they have identical banding arrangements in all five major polytene chromosomes (Carson et al., 1967). Despite this, the three species are readily distinguishable morphologically. The data presented show that distinct intraspecific population, differences in inversion frequency occur over very short linear distances.