The usefulness of a short-term azaserine [CAS: 115-02-6; diazoacetate serine (ester)]-rat model for the screening of retinoids (known chemopreventive agents) and the effect of two retinoids on the growth of azaserine-induced, presumptive preneoplastic foci of acinar cells were examined. At 14 days of age, male Lewis rats were each given injections of a single dose of 30 mg azaserine/kg body weight. These rats were weaned to test diets to which retinoids were added. At 4 months post initiation, pancreata were examined by quantitative stereologic methods to determine number and mean size of foci. Two phenotypically different populations of foci were observed and characterized as acidophilic or basophilic. Retinylidene dimedone and N-2-hydroxyethylretinamide decreased the number and size of the acidophilic foci but not the basophilic foci. The inhibition of growth of the acidophilic foci correlates well with the known effects of these retinoids in long-term carcinogenicity studies.