Human rhinoviruses (HRVs; family Picornaviridae), the most frequent causative agents of respiratory infections, comprise more than 100 distinct serotypes. According to previous phylogenetic analysis of the VP4/VP2-coding sequences, all but one of the HRV prototype strains distribute between the two established species, Human rhinovirus A (HRV-A) and Human rhinovirus B (HRV-B). Here, partial sequences of the RNA-dependent RNA polymerase (3D polymerase)-coding gene of 48 HRV prototype strains and 12 field isolates were analysed. The designated division of the HRV strains into the species HRV-A and HRV-B was also seen in the 3D-coding region. Phylogenetically, HRV-B clustered closer to human enterovirus (HEV) species HEV-B, HEV-C and poliovirus than to HRV-A. Intraspecies variation within both HRV-A and HRV-B was greater in the 3D-coding region than in the VP4/VP2-coding region, with the difference maxima reaching 48 % at the nucleotide level and 36 % at the amino acid level in HRV-A and 53 and 35 %, respectively, in HRV-B. Within both species, a few strains formed a separate cluster differing from the majority of strains as much as HEV-B from HEV-C. Furthermore, the tree topology within HRV-A differed from that for VP4/VP2, suggesting possible recombination events in the evolutionary history of the strains. However, all 12 field isolates clustered similarly, as in the capsid region. These results showed that the within-species variation in the 3D region is greater in HRV than in HEV. Furthermore, HRV variation in the 3D region exceeds that in the capsid-coding region.