The effect of barley supplementation with synthetic protected lysine (gelatine preparation) was investigated in the experiment caried out on 28 growing pigs. The aim of those protection was delaying of lysine absorption in the digestive tract. The control group (I) was fed with the mixture composed of ground barley and fish meal (15% crude protein, 0.78% lysine). Pigs of the other groups were fed with ground barley (the only protein feed in mixture) without lysine (group II), with free lysine (group III) or protected lysine addition (group IV). The fattening period lasted 90 days (initial live weight of pigs av. 21 kg). The form of lysine had no effect on the nitrogen balance results. However, the productive results of fattening found in group IV were significantly better than in group III and did not differ from control group (the final weight of pigs in following groups were, respectively: 70.6, 42.3, 59.0 and 65.8 kg, daily weight gains: 555, 241, 427 and 500 g, feed per 1 kg gain: 3.29, 6.33, 4.28 and 3.66 kg, digestible protein per 1 kg gain: 375, 475, 313 and 267 g). The results of the experiment showed that the supplementation of low-protein cereal diet with protected synthetic lysine could be purposeful.