INCLUSION CRITERIA:  Gr1. HIV-infected children with SAM  Age 6 months to 5 years Diagnosed with TB and first line TB treatment to be initiated or started less than 4 weeks prior to inclusion HIV-infection SAM as defined by WHO at the time of starting TB treatment Weight-for-height z-score (WHZ) < -3 SD, OR MUAC <11.5 cm or OR presence of bilateral pitting oedema of nutritional origin Ability to take drugs orally during the planned PK day Signed informed consent from parents or guardian  Gr2. HIV-infected children without SAM  Age 6 months to 5 years Diagnosed with TB and first line TB treatment to be initiated or started less than 4 weeks prior to inclusion HIV-infection Absence of SAM as defined by WHO at the time of starting TB treatment Weight-for-height z-score (WHZ) > -3 SD, AND MUAC >11.5 cm or AND absence of bilateral pitting oedema of nutritional origin Ability to take drugs orally during the planned PK day Signed informed consent from parents or guardian  Gr3. HIV-negative children with SAM  Age 6 months to 5 years Diagnosed with TB and first line TB treatment to be initiated or started less than 4 weeks prior to inclusion HIV-negative SAM as defined by WHO at the time of starting TB treatment Weight-for-height z-score (WHZ) < -3 SD, OR MUAC <11.5 cm or OR presence of bilateral pitting oedema of nutritional origin Ability to take drugs orally during the planned PK day Signed informed consent from parents or guardian  Gr4. HIV-negative children without SAM  Age 6 months to 5 years Diagnosed with TB and first line TB treatment to be initiated or started less than 4 weeks prior to inclusion HIV-negative Absence of SAM as defined by WHO at the time of starting TB treatment Weight-for-height z-score (WHZ) > -3 SD, AND MUAC >11.5 cm or AND absence of bilateral pitting oedema of nutritional origin Ability to take drugs orally during the planned PK day  NON INCLUSION CRITERIA:  Very ill or moribund children unable to take drugs orally or requiring nasogastric drug intake Severe anaemia (Hb < 6 g/dl), Severe renal impairment (DAIDS grade 3 and above) Severe hepatic impairment (DAIDS grade 3 and above) Children on second line TB drugs