The interaction between inbreeding and high-temperature stress was examined in the cactophilic fruit fly, Drosophila buzzatii. Embryos of four inbreeding levels (F = 0, F = 0.25, F = 0.375, F = 0.5) were either maintained at 25 degrees C throughout egg-to-adult development or were exposed to 41.5 degrees C for 110 min at an age of 20 h. Hatching, larva-to-pupa survival, pupa-to-adult survival, and egg-to-adult survival were estimated. Heat shock reduced hatching rates, but survival to adulthood for individuals that hatched was unaffected by the heat shock. Inbreeding reduced the proportion of eggs hatching in the 25 degrees C control group only. For larva-to-pupa and pupa-to-adult survival there was no interaction between inbreeding and stress. The effect of inbreeding on egg-to-adult survival was stronger in the 25 degrees C control group compared with the group exposed to heat shock. The results imply environmental dependency of inbreeding depression and suggest that stress tolerance may not always be reduced by inbreeding. The thermal microenvironment of cactus rots in the field was assessed by measuring temperatures inside 17 rots. Internal rot temperatures varied with a maximum temperature of 48 degrees C during the day. Selection for temperature tolerance in nature may have depleted genetic variation for this trait limiting the effect of inbreeding on thermal resistance.