Newly weaned piglet diets are normally highly digestible, and as such are composed of ingredients with high acid-binding capacities (Bolduan et al., 1988), which are potentially detrimental to the maintenance of a low gastric pH. The most active element effecting the phenomenon of acid-binding capacity (ABC) is calcium, and a high concentration in pig starter diets can significantly reduce post-weaning growth performance (Hardy, 1992). However, the mechanism by which ABC retards growth performance is largely unknown. Accordingly a preliminary study was designed to examine the effects of ABC on gut morphological characteristics such as villous height, width and crypt depth, together with digesta pH which is an independent factor influencing microflora colonisation.