A novel amino acid supplementation strategy was developed for enhancing the production of IL-2 (interleukin-2; as a model protein) by recombinant Escherichia coli BL21 (pET21a-hil2) in fed-batch high-cell-density cultures. The amino acids most needed and their amounts were determined using a stoichiometric model, and full factorial design experiments were conducted to determine the effects of single amino acids and amino acid mixtures on production. One of the most effective amino acid mixtures was found to be leucine, aspartic acid and glycine. This amino acid mixture was utilized for the production of IL-2 in batch and fed-batch fermentations. The amount of IL-2 produced increased from 403 to 722 mg/l and from 5.15 × 10³ to 8.08 × 10³ mg/l in batch and fed-batch cultures respectively. The results also revealed that the above amino acid mixture specifically increases IL-2 concentration in the cells.