SummaryNew ventilated caging systems for laborat ory animals were compared with conventional caging regarding allergen distribution, ergonomic suitability, cage environment and animal welfare. T his paper presents occupational health evaluations.Mice were placed in individually ventilated cage (IVC ) systems, a ventilat ed cabinet, and in cages on open shelves (conventional husbandry). T he IVC systems were studied at negative and positive air¯ow. Aeroallergens were sampled on ®lters (nˆ204, including controls) in undisturbed rooms and during cage changing. Concentrations of mouse urinary allergen (Mus m 1) in ®lter eluates were measured using sandwich ELISA. An ergonomic evaluation was performed with measurement of traction forces.Staff exposure during cage changing was high in all systems, range 116±4430 ng Mus m 1=m 3 . In undisturbed animal rooms, allergen levels were orders of magnit ude higher when using conventional caging compared with ventilated systems; P < 0.001. At positive pressure, both IVCs leaked allergen (median Mus m 1 concentration was < 0.08 ng=m 3 at negative, but 6.5 ng=m 3 (IVC1) and 0.8 ng=m 3 (IVC2S) at positive pressure). T he IVC systems had ergonomic disadvantages compared with the conventional husbandry and the ventilated cabinet, for instance with cages in unsuitable working heights.Ventilated husbandry solutions reduce levels of airborne allergen substantially at negative pressure, but are ergonomically less suitable. To prevent allergen exposure during cage changing, we propose that this procedure should be performed under ventilated conditions. Producers and users must cooperate in optimizing anim al caging systems for both anim als and staff.