Evolutionary relationships of circulating H3N2 influenza A viruses sampled in Denmark from 1999 to 2006. The nucleotide coding region trees were generated with maximum parsimony, heuristic random branch swapping search (neighbor joining and maximum likelihood analysis revealed the same tree topology). Bootstrap values of 1000 resamplings in per cent (>70%) are indicated at key nodes. H3N2 HA and NA trees are rooted to A/Beijing/353/89 and A/Beijing/32/92. Reference sequences referred to in the text are shown in bold. The A/Fujian/411/02(H3N2) reference sequence is represented by A/Wyoming/03/03.