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Two methodologies widely used in digestibility trials for determination of acid-insoluble ash (AIA) in feeds and faeces are the procedure described by Vogtmann et al., 1975, (VO; Br. Poult. Sci. 16, 531) based on the boiling of the complete sample (4N HCl for 30 min), followed by ashing at 600°C for 6 h, and the procedure described by Van Keulen and Young, 1977, (VK; J. Anim. Sci. 44, 282) based on the sequential analysis of DM, ash, and boiling (2N HCl for 5 min) to determine AIA. In our test we used 12 experimental diets of similar nutritive value to determine apparent retention of nutrients and the AMEn by both techniques in 18 d-old broilers. The main difference among diets was the cereal used (corn vs. rice), the type of processing of the cereal (raw vs. heat processed), and the inclusion of a fiber source (none vs. 3% oat hulls vs. 3% soybean hulls) and all of them included 1% celite an additional indigestible marker. Each treatment was replicated three times (9 birds caged together). The AIA values of feeds and excreta were lower when determined by VK than when determined by VO (1.693 vs. 1.748% DM for diets and 6.655 vs. 6.961% DM for excreta; P < 0.001) but no interactions of technique x dietary treatment were found. The correlation coefficient of the AIA content of feeds and excreta between VO and VK techniques was good (r > 0.99). Nutrient digestibility and AMEn of the diets were lower when calculated with the VK technique than when calculated with the VO technique (74.6 vs. 75.0% for DM, 79.1 vs. 79.5% for OM, and 3,022 vs. 3,033 kcal/kg for AMEn; P < 0.05) but no interactions between techniques used for AIA determination and dietary treatments were observed. We concluded that either technique is acceptable to determine the apparent retention of nutrients and the AMEn of diets in poultry experiments. [ABSTRACT FROM AUTHOR]