Abstract: The subject of the present invention is a nucleic acid probe containing a nucleic acid sequence, wherein the said sequence is linked at its 5' end, via a divalent bifunctional chemical "arm" L, to a "labeling component" M, M being a synthetic or natural molecule which is directly or indirectly detectable in a non-isotopic manner, according to the formula I: ##STR1## in which J=H or OHn denotes the number of nucleotides from 1 to 100,000B is a purine or pyrimidine nucleic acid base, which varies according to the nucleotide, as appropriate.The subject of the invention is also a process for preparing such probes, employing an intermediate compound consisting of a nucleotide synthon of formula IV ##STR2## in which J, B, L and R.sub.1 have the meanings given above, B optionally being protected,R.sub.2 denotes H or any phosphorylated group, optionally protected, suited to the introduction of the compound of formula IV at the 5' end of another nucleotide, for a given type of internucleotide-assembling synthesis.