To improve the quantitative and qualitative hair growth, skin structure and/or nail regeneration, a mixture of proline and carrier substances is used, which may additionally contain at least one of the four amino acids valine, leucine, isoleucine and/or glycine. The mixture is prepared for oral administration. The mixture may contain, as additional additives, ATP, biotin, cysteine, lysine, methionine, and others. The preparation may furthermore have a positive effect on the stamina, muscle build...