A survey of the prevalence of laboratory animal allergy to rats, mice, guinea pigs and rabbits among sixty-nine animal workers and 308 other subjects on a pharmaceutical research site revealed a 22% prevalence of laboratory animal allergy among the animal workers. The overall prevalence of atopy was 67% in persons with allergy to laboratory animals. This was significantly greater than the 31% prevalence in other animal workers. Skin-prick tests and specific IgG and IgE assays to urinary protein extracts strongly correlated with the occurrence of laboratory-animal allergy and would appear to have diagnostic value. However, a number of clinically diagnosed laboratory-animal-allergy subjects gave no evidence of immunological response to the urinary allergens and wider diagnoses may have to be applied in these cases.