A micelle-forming new dipeptide, Boc-Lys(Z)-Tyr-NHNH2, has been synthesised in our laboratory and characterised. The critical micelle concentration (c.m.c.) of this peptide in aqueous solution has been determined at different temperatures using UVâ VIS, fluorescence and FTIR spectroscopies, and conductometric techniques. The c.m.c.s obtained by these methods are in good agreement with each other. The effects of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) on the micelle formation of the dipeptide have also been studied. The aggregation numbers of the peptide and peptideâ surfactant complexes have been determined by fluorescence techniques using the Mg salt of 8-anilino-1-napthalenesulfonic acid (ANS) and N-cetylpyridinium chloride (CPC) as probe and quencher, respectively. The enhancement of water IR intensity (at 3410 cm^{â 1}) in the peptide at concentrations above the c.m.c. during FTIR measurements suggests the presence of intermolecular H-bonding of the peptide micelles.