Abstract: Restriction maps of ribosomal DNA repetypes of the three putative slow lorises species,Nycticebus coucang,N.intermedius and N.pygmaeus,were constructed with 15 restriction endonucleases and 28S,18S rDNA probes cloned from human.The site numbers mapped on the non-transcribed spacers for N.coucang,N.intermedius,and N.pygmaeus,were 23,24,and 24 respectively.N.coucang differs from N.intermidius at 13 sites,and 14 sites from N.pygmaeus.There are only one site difference between N.intermedius and N.pygmaeus.The sequence divergence between N.coucang and N.intermedius was estimated as 12.65%,and that between the former and N.pygmaeus was 14.24%.However,N.intermedius and N.pygmaeus have only 0.71% sequence divergence.Integrating information from morphology,karyotype,mitochondrial DNA and ribosomal DNA variation,we refer to the hypothesis that there are two valid species in the genus Nycticebus,namely,N.coucang and N.pygmaeus while N.intermedius may be at the level of semispecies of N.pygmaeus at the most.The giant difference between N.coucang and N.pygmaeus implies that the former has strongly diverged from the latter.