Doses of 3 mg/kg Ro 10-9359 (in arachis oil) were daily administered to adult female Wistar rats by gastric tube for a period of 10 days. Control animals received corresponding quantities of arachis oil only. The body weight of all rats was registered daily. Samples of jejunum and ileum were processed for quantitative histochemical analysis of neutral alpha-glucosidase kinetics and for three-dimensional evaluation of the mucosal architecture. In addition, mucosal scrapings were prepared from these intestinal segments, and the specific sucrase activity was determined. For each animal data were pooled and analyzed by Wilcoxon (Wn) test. Body weight and all registered parameters in the jejunum of treated animals remained unchanged as compared to the controls. In the ileum, however, we found under aromatic retinoid an increase of sucrase activity (P = 0.02) and of mucosal surface per unit serosal area (P less than 0.05). The hydrolytic activity of neutral alpha-glucosidase (Vmax) showed a clear trend to increase at both the villus base and apex, whereas the apparent substrate affinity (Km) remained unaltered. Our results show that, in closes of 3 mg/kg/day, aromatic retinoid induces (1) an increase in mucosal surface area, apparently due to hyperproliferation of the absorptive epithelium in ileum, which could facilitate its absorptive capacity and (2) an increase of specific sucrase activity, which could result in an enhanced carbohydrate assimilation. These findings indicate that Ro 10-9359 in addition to its effects on keratinizing epithelia exerts a distinct influence on the structure and function of the intestinal epithelium.