Using the sliced intestine method, we studied in vitro the effects of long-term fasting (4 and 8 weeks) on the accumulation of 0.5 and 10 mM glycine in the mid- and hindgut of the trout. Increased glycine accumulation during fasting was noted when accumulation was calculated per gram of intestinal dry weight, per milliliter of cellular water, but especially per gram of mucosal tissue. The glycine tissue to medium ratios are also higher in fasted intestines, revealing an enhancement of the active pathways of the amino acid transport. After 4 weeks of fasting, the increased glycine accumulation is greater in hindgut, especially for the lowest glycine concentration (0.5 mM). With the highest concentration (10 mM), the effects of fasting similarly decrease in intensity and affect in the midgut and hindgut. After 8 weeks of fasting, the differences between fed and fasted intestines tend to be fewer, probably because of a progressive attenuation of the effect of fasting on the active pathways of glycine accumulation.