Derivatives of 7-aminocoumarins are the most extensively utilized labeling reagents for preparing brightly blue fluorescent conjugates of proteins and nucleic acid. Labeled amino acids are detected with visible semiconductor laser fluorometry using second harmonic emission (415 nm) of the near-infrared semiconductor laser. Arginine, proline, serine and glycine have been detected with detection limits around 100 amol levels. The fluorescent-labelling better matches the excitation-wavelength of standard blue lasers than conventional fluorescein-isothiocyyanate.