Working with laboratory animals in research is correlated with a high risk of developing laboratory animal allergy, and 5-40% of researchers exposed to animals develop an allergy within the first year. We describe three cases of asthmatic allergy in the same research group within a brief period of time. The research facility was an old hospital building which had not been adequately rebuilt to support animal facilities. Both the ventilation system and the design of the facility were inadequate. We compiled the case histories in the hope of preventing this well-known, but often not considered, hazard when building or reconstructing research facilities intended to house laboratory animals.