During the course of a "dry" season dengue vector survey, indoor and outdoor household wells were sampled for the possible presence of immature mosquitoes and copepods. With a simple floating funnel trap, Aedes aegypti immature stages were captured in over 33% of the sampled wells (n = 93) during a 24-h trapping period per well. Average number of larvae (all instars) per positive well was 8.8 (range 1-63). Positive wells varied in depth from 2.7 to 14.7 m (8.8-48.2 ft), with a mean of 7.9 +/-SE 0.5 m in well rim to water surface. Only 4 wells (4.3%) contained Culex quinquefasciatus larvae. Only 1 of 31 infested wells contained both species. Aedes albopictus was not detected in any of the wells. Cyclopoid copepods were captured in 15% of the wells. No significant difference was found between positive and negative wells with regard to the physical characteristics (inside diameter, distance to water level) or the depth and volume of water held at the time of sampling. A significant association was found between wells positive for larvae and numbers of other positive containers in the vicinity of the wells. In general, wells containing copepods had fewer larvae present in the trap, possibly indicating some level of natural population regulation of Ae. aegypti occurring in the well; however, this association was not significant. Preliminary results indicate that wells in Yogyakarta serve as important permanent habitats for Ae. aegypti, especially during the dry season.