Abstract Population trends of house dust mites in house dust on floors and mattresses were studied in 11 homes in Bogota, Colombia, over a period of 10 months. Among the pyroglyphids, species composition was: Dermatophagoides pteronyssinus (Trouessart) 84. 5%; Euroglyphus maynei (Cooreman) 14. 9%; and Dermatophagoides farinae Hughes<1%. The data revealed that mite populations prevailed throughout the study period in both niches. The mattress populations were higher at all times than those on the floor. The mattresses showed 2 discrete peaks in October and May, whereas the floor populations had greater fluctuations. The densities of all stages were lowest from December to March. Population density of D. pteronyssinus was higher than that of the other 2 species. An analysis of population age structure for both D. pteronyssinus and E. maynei revealed adult stage density was higher than the immatures. The density of dead and live mites in each niche varied, but the proportion of live individuals never exceeded 36% of the population. The floor population had the greatest percentage of live mites most of the time.