The nature, frequency and symptoms of laboratory animal allergies (LAA) were explored in 110 persons having contacts with laboratory animals and working in research laboratories at Zürich University Hospital and institutes. 20.9% of these persons were actually suffering from a laboratory animal allergy, a percentage corresponding to international reports in the literature (12-27%). 82.6% of persons with LAA were atopic subjects. In a group without LAA we found an atopic disposition only in 25.3%. The commonest signs of LAA were a combination of rhinoconjunctivitis with bronchial asthma and with contact urticaria in 43.5% over-all. Rats and mice were the laboratory animals most contacted and they represented the largest number of sensitizations. The interval between the beginning of exposure and onset of the symptoms of LAA ranged between a few months and many years. In general, the time space is much shorter in atopic subjects than in non-atopic persons. Skin tests gave better and more precise results in the detection of a LAA than in vitro examinations. This means that investigations with RAST (PHARMACIA) were less sensitive than the prick multitest (STALLERGENES). The last-mentioned can be recommended as very good for serial allergological examinations. The new Phadiatop-test (PHARMACIA)--in the study we obtained positive results in 38.5%--is a sound and most specific examination for discrimination between atopic and non-atopic disposition. Determination of total IgE was of less value.