L-Lysine displays new absorption and fluorescence features at high concentrations (similar to 0.5 M) in aqueous medium. A new absorption peak was detected around similar to 270 nm (epsilon = 0.34 M-1 cm(-1)). Blue fluorescence (similar to 435 nm) was visible on excitation at 355 rim. The above features which were concentration dependent are attributed to likely aggregates Of L-lysine.