SUMMARYIn a group of Australian Chironomus species, sex determining regions involved in male heterogarnety have been found at a minimum of five different chromosomal locations. In one case, Ch. oppositus A, sex determining regions have been identified on two different chromosomes. It is uncertain whether this is a polymorphism or indicates the existence of multiple sex determining regions. It is argued that all the published data on sites of male determining regions are compatible with the five locations found in this study. On the basis of the postulated phylogeny of the studied group, the location of the sex determining regions would appear to have changed during speciation in all cases except one. The significance of these changes in location during the speciation process is discussed.