Phylogenetic tree based on 417 bp of LTR region sequenced from 82 viral strains of HTLV-II/STLV-II. Shown is one of two equivalent trees obtained by ME estimated by NJ. A 50% majority rule consensus of 8610 trees (length = 577; C.I. = 0.797) and a ML tree (ln likelihood = −1987; 26,882 trees examined) corroborate the topology depicted. Numbers in italics denote bootstrap proportions in support of adjacent node (NJ/MP). Both NJ and MP trees were reconstructed using PAUP* (by permission of D. Swofford). Unrooted NJ trees were based on the Tamura-Nei (1993) model of substitution and negative branch lengths were allowed using the tree-bisection-reconnection swapping algorithm. Conditions for MP heuristic search used unordered characters of equal weight, gaps were treated as a fifth base, and trees were rooted by the midpoint method. ML tree reconstructed by PHYLIP35 (Felsenstein 1993) subroutine DNAML. Asterisks (*) indicate Amerindian strains. Accession numbers for all 82 strains used in this analysis are listed athttp://rex.nci.nih.gov/RESEARCH/basic/lgd/front_page.htm.