We describe how much of the variation in rat urinary aeroallergen (RUA) levels may be explained by differences in site and exposure group in research establishments and we identify task categories associated with high RUA levels. In this population 73% of the variability in RUA levels could be explained by exposure group, site and their interaction term. Exposure group alone explained the majority of the variation (69%). The task category associated with the highest RUA level was cleaning out, followed by indirect contact with rats and handling rats. The task categories associated with the lowest levels were slide production, post mortem and experiments. These results may help choose appropriate exposure measures for epidemiological studies in research establishments in the future and may help reduce the incidence of laboratory animal allergy.