Our objectives were to describe and compare the seasonal variations in microclimatic conditions in domestic and peridomestic ecotopes infested by Triatoma infestans, the main vector of Chagas disease, in rural northwestern Argentina. Using data loggers for 4-7 consecutive days in October 2000, February, May and August 2001, microsite (interior of thatched roofs) and ambient temperatures or relative humidity (RH) were recorded simultaneously and compared with an external reference. The damping effects on microsite temperature and ambient RH increased successively from the goat corral to the chicken coop or pig corral, to the storeroom or human habitation. In the interior of the thatched roofs of the habitation and storeroom, average external minima were increased by +5.0 to +5.6 degrees C in all seasons, and average external maxima were decreased by -4.3 to -5.6 degrees C in October-May and -10.6 degrees C in August. On average, the human habitation damped extreme temperatures by 8 degrees C over a wider range than previously reported. The interior of the thatched roofs of the pig corral and chicken coop exerted intermediate damping effects that varied over seasons, whereas the goat corral's thatch showed little or no damping effects at all. The adobe-and-thatch habitation and storeroom presented nearly optimal and more suitable conditions for T. infestans populations than other open structures housing animals. Global climate changes are expected to affect peridomestic populations of T. infestans much more than domestic bug populations, provided other local conditions are held constant. Heterogeneous habitat conditions are expected to affect T. infestans population parameters, dispersal, control and infection with Trypanosoma cruzi.