The aim of this study was to determine the effect of Bio-Mos® (Alltech Inc.), with or without the addition of a soluble mannan (MRF) (Alltech Inc.) on gastrointestinal health and performance of broiler chickens. A trial was conducted using seven different dietary treatments. It consisted of a negative control, 2 levels of Bio-Mos® (2 g/kg and 4 g/kg), 2 levels of MRF (0.1 g/kg and 0.2 g/kg) and 2 treatments combining the cell wall preparations (2 g/kg Bio-Mos® + 0.1 g/kg MRF and 4 g/kg Bio-Mos® + 0.2 g/kg MRF). Day-old male broiler chicks were randomly allocated to the seven treatments and the trial extended over a 15 day period, upon which two chicks from each replicate were sacrificed and ileum samples taken. Results showed that the cell wall preparations had a numerically positive, but statistically non significant effect on feed conversion ratios. Histology results revealed significantly greater goblet cell densities and sizes for chicks receiving cell wall preparations than those of the control treatment chicks, while villi width and height measurements indicated no differences between treatments. From the results of this study it appears as if yeast cell wall preparations can contribute to the gastrointestinal health and performance of broiler chickens by affecting mucus secreting goblet cells in a favourable manner.