In conventional and repeatedly re-alkalized cultures of two lactic acid bacteria, the effects of five amino acids and their interactions on biomass and bacteriocin (nisin and pediocin) production were studied. Nisin production was stimulated by cysteine and tryptophan, and depressed by proline. Equations describing biomass production in Lactococcus lactis, and biomass and pediocin productions in Pediococcus acidilactici, contain numerous terms with three and four variables, indicating that none of the amino acids seems to play a relevant individual role. Stimulation due to the pH-stepwise profiles exceed significantly those of the most effective amino acid combinations and promote much faster consumption of some amino acids. Since a pH-stepwise Culture can be considered as a series of successive incubations, each starting up in presence of the metabolic products from the preceding step, these results are more compatible with an auto-stimulatory mechanism rather than a nutritional phenomenon. (C) 2003 Elsevier Inc. All rights reserved.