The goal of this study was to evaluate how two new hydrolysates from poultry by-products act on ten lactobacilli growth kinetics when supplemented to the growth medium. These effects were compared with ones induced by two most common commercial hydrolysates, i.e., tryptone and peptone. Growth medium, supplemented with one of new hydrolysates, 78T, as only nitrogen source, can sustain the maximum growth rate and the biomass yield in the same way of MRS, reach of different nitrogen sources. Moreover aminopeptidase activities (AA) of each strain were determined to investigate the effect of the growth condition on the modulation of aminopeptidase pattern. Five cell extracts of each ten strains, obtained from their cultivation in MRS and in the presence of the two common hydrolysates and the two new ones, were considered. AA was investigated against five different chromogenic substrates: beta-naphthyl amide derivatives of l-anomers of leucine, lysine, proline, glycine-proline, and phenilalanine-proline. A great variability of AA was observed among the strains: also strains belonging to the same species showed peculiar AA profile.