INCLUSION

1. Male or female subjects >=18 years of age with HIV-1 infection and chronic liver disease as reflected by a documented biopsy with hepatic fibrosis present.

2. a. Participants must be receiving nevirapine 200 mg twice daily as part of a stable ARV regimen for a minimum of 6 weeks prior to trough level sample collection.

   b. Participants receiving nevirapine 400 mg once daily as part of a stable ARV regimen for a minimum of 6 weeks, who are willing to switch to nevirapi0 mg twice daily for a minimum of 14 days prior to trough collection.

3. Participants must have uoxylin and Eosin (H and E) stained slide and one trichrome stained pathology slide available at the time of enrollment. There is no time restriction on liver biopsy slides that pathologically confirm the presence of cirrhosis. The presence of cirrhosis must be documented on the liver biopsy report.

EXCLUSION

1. Current (within the past 4 weeks) HIV antiviral therapy with other NNRTI's.

2. Concurrent use (within the past 7 days) of any of the following:

   1. Systemic azole antifungal agents (fluconazole, itraconazole, ketoconazole, etc.)
   2. Clarithromycin
   3. Rifampin
   4. St John's Wort
3. Inability to provide a blood sample.
4. Patients who have evidence for hepatic or other encephalopathy above Grade 1
5. Patients with renal failure who require dialysis.
6. Pregnant and/or breast feeding women..