In a prospective study of laboratory technicians, selected indicators of allergy and atopy were studied in an attempt to determine predictors of laboratory-animal allergy (LAA). Laboratory technicians underwent spirometry, methacholine provocation tests, and blood sampling, and responded to a questionnaire during training and after 2 years' work. Among 38 laboratory-animal-exposed subjects, total IgE before exposure gave the best correlation (P < 0.01; Mann-Whitney U-test) to reported symptoms caused by laboratory animals (n = 8) at follow-up. The prevalence of atopy and allergic symptoms had increased in exposed technicians at follow-up, but this was also found among unexposed matched referents (n = 36 pairs). One subject in the exposed group reported asthma before exposure, compared with seven at follow-up (P < 0.05; Fisher's exact test). However, the prevalence of asthma had increased from two to six (not significant) also among unexposed technicians. There were no significant differences between the groups in any measured variable at follow-up. Among 43 subjects who later worked with laboratory animals, 21% had a positive skin prick test for common allergens, as compared with 37% among 112 without animal exposure (P = 0.06; chi2 test), suggesting selection for laboratory animal work.