This Phase IIb study in HIV-infected antiretroviral naive adult subjects will include a dose-ranging evaluation of GSK1349572 10mg, 25mg and 50mg once daily blinded doses and a control arm of open label efavirenz 600mg once daily. Background ART for all study subjects will be chosen by the investigators and will be either Truvada or Epzicom/Kivexa. Data from the three doses of GSK1349572 will be compared on the basis of antiviral activity, safety/tolerability and pharmacokinetics over 16-24 weeks.