We investigated the occurrence of diarrhoea in postoperative patients on tube feeding, with or without soyfibre supplementation. The patients also received antibiotic treatment. 60 postoperative patients were assigned to either a fibre free formula diet (FFF) or a soyfibre supplemented formula diet (SSF). The tube feeding was supplied continuously through a nasogastric or a jejunal tube (mean volume 1775 ml a day). The consistency and frequency of the bowel evacuations were recorded for a period of 5 days. A daily diarrhoea score (DS) was obtained by adding a consistency score (formed stools 1, loose 3, and watery 5 points) for every evacuation. The major finding of this study is that the total DS of the FFF group was 1.7 times higher than the SSF group (ANOVA, p = 0.05). We conclude that soyfibre enriched tube feeding has a beneficial and significant influence on the occurrence of diarrhoea in a selected group of postoperative patients.