The hypothesis that an increase in luminal viscosity would result in reductions in performance parameters, digesta passage rate and frequency of reverse peristalsis was tested. Chickens were fed diets containing varying quantities of guar gum, alginic acid or corn starch to influence digesta viscosity. The two guar gum treatments yielded the highest intestinal viscosities mirrored by very high feed conversion ratios, low starch digestibility and, for birds exposed to the highest level of guar gum, very low weight gain compared to the control birds. An association between a rise in ileal viscosity and low transit times was recorded; however at the highest viscosity, transit rates were significantly less than the control. Cloacally administered Cr-EDTA was retrieved from the gizzards of birds in all treatments. The marker was recovered in greater amounts in birds exhibiting lower ileal viscosities, with the exception of birds from the high level guar gum group, displaying faster passage rates and lower ileal viscosities.