Laboratory animal allergy is a serious health problem. We examined several possible allergen-reducing strategies that might be effective in the working mouse room. Ambient allergen concentrations were measured when mice were maintained under several conditions: conventional housing versus ventilated cage racks operated under negative or positive pressure. We found that housing mice in ventilated cages operated under negative pressure and using ventilated changing tables reduced ambient mouse allergen (Mus m 1) concentrations tenfold, compared with values when mice were housed in conventional caging and using a conventional (non-ventilated) changing table. Housing mice in positively pressurized cages versus conventional cages did not reduce ambient allergen values. Cleaning mouse rooms at an accelerated frequency also did not reduce ambient Mus m 1 concentration. We also quantified ambient allergen values in several areas of The Jackson Laboratory. A facility-wide survey of Mus m 1 concentrations indicated that allergen concentrations were undetectable in control areas, but ranged from a mean (+/- SEM) 0.11 +/- 0.02 ng/m3 to 5.40 +/- 0.30 ng/m3 in mouse rooms with different cage types. The percentage of animal caretakers reporting allergy symptoms correlated significantly with ambient allergen concentrations: 12.9% reported symptoms in the rooms with the lowest allergen concentration (0.14 +/- 0.02 ng/m3), but 45.9% reported symptoms in rooms with the highest concentration (2.3 +/- 0.4 ng/m3). These data indicate that existing technology can significantly reduce exposure to laboratory animal allergens and improve the health of animal caretakers.