A two-arm, as well as a two-period pharmacokinetic study in HIV-infected children with and without TB will be performed at the Komfo Anokye Teaching Hospital (KATH), Kumasi, Ghana. Eligible participants will include children aged 3 - 14 years with HIV with or without TB coinfection, ART-naïve and eligible to initiate ART. The ART regimen will consist of the WHO recommended weight-band dosing of efavirenz (10-13.9kg - 200 mg; 14-24.9kg - 300mg; 25-39.9kg - 400 mg and > 40Kg - 600 mg), plus ZDV 180 - 240 mg/m2 and 3TC 4 mg/kg twice daily. Tenofovir may be used in place of ZDV. Standard anti-TB therapy will be prescribed to the co-infected patients and will start immediately upon TB diagnosis.