Herein we present experimental evidence of the strong surface plasmon enhancement of two-and three-photon absorption of Hoechst 33 258 (2'-(4-hydrophenyl)-5-(4-methyl-1-piperazinyl)-2,5'-bis(1H-benzimidazole )) pentahydrate in an aqueous solution containing activated gold colloid. The 480-fold enhancement in two-photon absorption and 30-fold in three-photon absorption are predominantly attributed to the electricfield enhancement via surface plasmon resonance. The greater enhancement observed in two-photon absorption is due to the characteristic two- and three-photon absorption cross-sections of the dye.