The syntheses of three novel functionalized tricarbocyanine dyes aredescribed. These dyes containingisothiocyanate and succinimidyl ester functional groups are reactivetoward primary amines and canbe used as fluorescent probes for biologically pertinent compounds suchas amino acids andfunctionalized dideoxynucleotides. The absorption and fluorescencemaxima occur in the near-IR regionof the spectrum (770-810 nm). The succinimidyl ester proved tobe very sensitive to hydrolysis andwas generated in situ to label amino acids. Theisothiocyanates were less susceptible to hydrolysisand were conjugated using organic modified [40% (v/v) acetonitrile]buffers to amino acids. A dyewith an alkyl isothiocyanate moiety showed conjugation toamino-functionalized dideoxynucleotidetriphosphates.