mtDNA NADH dehydrogenase subunits 2 and 3 and nDNA β-fibrinogen intron 7 sequence data puts it closer to (but still well distant from) the Streaked Bulbul (Ixos malaccensis).
However, using mt and nDNA sequences of increased length, Sorenson et al. in 2003 noted that all three previous DNA studies were apparently flawed due to errors in methodology, small sample size, and sequencing errors; their study strongly suggested against a close relationship between the Hoatzin and cuckoos or turacos.