Infectious diarrhoea is a major problem in both children and piglets. Infection of enterotoxigenic Escherichia coli (ETEC) results in fluid secretion and electrolyte losses in the small intestine. In the present study the effect of processed and fermented soyabean products on net absorption during ETEC infection was investigated. Soyabean was processed into an autoclaved, a cooked and a mould-fermented (tempeh) product. The soyabean products were pre-digested and the effect of the products on net absorption in the small intestine of piglets was studied. Pairs of small-intestinal segments, one non-infected and the other ETEC-infected, were perfused simultaneously with the different products during 8 h. Net absorption of fluid, DM, Na, chloride, K and total solutes was determined. Net fluid absorption was highest for cooked soyabean followed by autoclaved soyabean and tempeh as a result of the osmolality of these products. In ETEC-infected segments, cooked soyabean and tempeh showed minor fluid losses (27 (SE 23) and 43 (SE 20) microl/cm(2), respectively) compared with the saline control (260 (SE 23) microl/cm(2)). Tempeh resulted in a high uptake of solutes. Processed soyabean products, particularly cooked soyabean and tempeh, are beneficial in maintaining fluid balance during ETEC infection. Additionally, tempeh showed high DM and total solute absorption. Therefore, particularly, tempeh may be beneficial in the case of post-weaning diarrhoea in piglets and possibly in children as well.