Off-host survival of the northern fowl mite, Ornithonyssus sylviarum (Canestrini & Fanzago) (Acari: Macronyssidae), and the chicken body louse, Menacanthus stramineus (Nitzsch) (Phthiraptera: Menoponidae), was studied at 12 combinations of temperature (15, 21, 27, and 33°C) and humidity (31, 65, and 85% RH). Mite protonymphs and louse third instars survived longer on average than the respective adult stages. Higher temperatures significantly reduced survival of adult and immature stages of both ectoparasites, whereas relative humidity had significant effects on O. sylviarum (especially protonymphs) but not M. stramineus. The LT₅₀ values for adult northern fowl mites ranged from 1.9 (at 33°C, 31%RH) to 8.3 d (at 15°C, 85%RH), LT₅₀ values for mite protonymphs ranged from 2.0 (at 33°C, 31%RH) to 18.1 d (at 15°C, 85%RH), LT₅₀ values for adult lice ranged from 0.5 (at 33°C, 31%RH) to 1.7 d (at 15°C, 65%RH), and LT₅₀ values for nymphal lice ranged from 1.2 (at 33°C, 65%RH) to 3.3 d (at 21°C, 31%RH). Maximum survival of the northern fowl mite was up to 35 d for adults and 29 d for protonymphs. Maximum survival for the chicken body louse was 3.3 d for adults and 5.8 d for nymphs. The data provide minimum guidelines for leaving poultry houses vacant long enough to allow ectoparasites to die before introduction of subsequent new flocks.