Abstract: A method for the detection of a nucleotide sequence of a nucleic acid in a sample. The method comprises the steps: (i) contacting under hybridization condition the single stranded form of the nucleotide sequence with a single stranded nucleic acid probe, in which plurality of rare earth metal chelate groups is covalently linked via a water-soluble polymer of non-nucleic acid structure to a nucleotide acid that as one of its strand has the nucleotide sequence to be detected and as the other strand the nucleotide sequence of the probe, and (ii) detecting the formation of double stranded nucleic acid. The plurality of rare earth metal chelate groups have at least one metal ion selected from the group consisting of Eu.sup.3+, Sm.sup.3+, Tb.sup.3+ and Dy.sup.3+ as the chelated rare earth metal. The probes as given above are also claimed.