The effects of different fiber sources on feed intake, weight gain and digestibility of fiber were examined in guinea-pigs fed pelleted diets containing alfalfa meal, oaten hay, beet pulp and commercial hay cubes mixed with a basal diet at ratios of 3:1 (75% in the diet), 1:1 (50%) and 1:3 (25%). The basal diet contained 50.0% corn, 4.1% wheat, 22.1% wheat flour and 17.7% corn gluten meal. Food intake increased as the amount of fiber source was increased, but not in the case of beet pulp. The most digestible fiber (ADF and NDF) was that of beet pulp. Apparent digestibility of dry matter decreased with increasing ratios of fiber source to the basal diet for all fiber sources, but fiber and crude protein digestibilities varied and depended not only on the ratio of fiber to the basal diet but also on the source of the fiber.