A population of 101 laboratory technicians handling laboratory animals was studied with regard to predisposing factors for allergy. Twenty-seven had symptoms indicating laboratory animal allergy (LAA); of these, nine had asthma and were skin prick test positive for animal allergens. The LAA asthmatics had an increased frequency of a family history of allergy (relative risk, RR = 3.8); the predictive value was 0.27. There was also an increase of skin prick positivity against common nonanimal allergens (RR = 15); the predictive value was 0.60. All persons with marked positive skin prick tests (greater than or equal to +2) to environmental allergens had developed animal-test-positive LAA asthma. In 56% of the LAA asthma cases the serum IgE levels were elevated (greater than 100kU/L). In preemployment screening of susceptible individuals two important selection criteria emerged, viz., family history of allergy and positive skin prick reactions against environmental allergens.