The effects of potato protein concentrates (PPC) differing in dietary solanidine glycoalkaloids (SGA) and trypsin inhibitor activity (TI), and of potato sprouts with differing SGA levels, were studied in rats. In Experiment 1, semi-purified isoprotein diets containing casein or one of six PPC contributing from 116 to 439 mg SGA · kg^–1 and from 0.13 to 0.45 mg · g^–1 of TI activity, were used. Weight gain was significantly greater on the diet containing PPC with low SGA and low TI than on PPC with high SGA and moderate TI contents, and also higher than on casein. Weight gain was also slightly depressed on diets with the highest TI activity. Substitution of PPC for casein resulted in lowering the pH of caecal digesta and increasing short-chain fatty acids concentration. Feeding diets with the greatest SGA content induced depression of protein and organic matter digestibility while diets with the greatest TI activity decreased protein digestibility but did not affect pancreas weight. In Experiment 2, a commercial rat diet, supplemented with increasing amounts of potato sprout meal providing SGA in the range from 0 to 300 mg · kg^–1, was used. Neither growth performance, organ weights, caecal parameters, nor enzyme activities were affected by the diet. It is postulated that the less evident response of rats to SGA in the natural ingredient than in the semi-purified diet was due to the attenuating effect of more intensive bacterial fermentation. Potato trypsin inhibitor should be considered as an antinutritional factor in PPC; interactive effects of SGA and TI are presumable.