Average absorbed dose values were calculated in various small laboratory animals (mouse, rat, guinea pig), using an albedo code, and the uniformity of the irradiation was studied. A plane source emitting neutrons with a cosine distribution was used. The neutron spectrum used was that measured in the irradiation facility of the Hungarian Research Reactor. Infinite-length cylinders with radii 1.25, 2.5, and 3.3 cm were used for calculation. The average absorbed dose was 85.2, 72.1, and 64.9% of the free-in-air kerma. None of the irradiations was uniform when unilateral irradiation was assumed. A uniform, Class A irradiation ($D_{{\rm max}}/D_{{\rm min}}<1.15$) could not be achieved in rats and guinea pigs if only bilateral irradiation or rotation was used. With various field-shaping filters, a very uniform irradiation may be performed, with$D_{{\rm max}}/D_{{\rm min}}\leq 1.05$, in all three types of animals. Present calculations were compared with other values (measured or calculated) published in the literature.

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