Experiments were designed to determine whether competition occurred between larvae of Aedes (S.) albopictus Skuse and A. (S.) polynesiensis Marks, with a resultant suppression in the development of one of the species. Larvae were reared at various densities and food supplies in single and mixed populations. Results showed that A. albopictus was superior to A. polynesiensis in that the larvae grew more rapidly, the survival rate to the adult stage was higher, and in general the adults were somewhat larger as determined by dry weight. The differences between the 2 species with respect to these characteristics became more marked at the higher densities of competing larval populations.