1. To investigate the relative bioavailability (BA) of improved tablet formulation candidates to determine which formulation will be developed for use in late Phase II and Phase III clinical trials
2. To investigate the relative BA of the pediatric suspension, compared to the current 1B formulation
3. To investigate the bioequivalence (BE) of BILR 355 BS in two tablet strengths; three 25mg tablets vs. one 75 mg tablet, current 1B formulation

Inclusion Criteria:

1. Healthy HIV negative adult male volunteers
2. Age ≥18 and ≤ 60 years
3. BMI ≥18.5 and BMI ≤29.9 kg/m2
4. Ability to give signed and dated written informed consent prior to admission to the study in accordance with Good Clinical Practice (GCP) and the local regulations

Exclusion Criteria:

1. Gastrointestinal, hepatic, renal, respiratory, cardiovascular, metabolic, immunological or hormonal disorders
2. Surgery of gastrointestinal tract (except appendectomy)
3. Diseases of the central nervous system (such as epilepsy) or psychiatric disorders or neurological disorders
4. History of relevant orthostatic hypotension, fainting spells or blackouts
5. Chronic or relevant acute infections
6. History of allergy/hypersensitivity (including drug allergy) which is deemed relevant to the trial as judged by the investigator
7. Intake of drugs with a long half-life (>24 hours) within at least one month prior to study drug administration and during the trial
8. Use of drugs within 10 days prior to administration or during the trial which might reasonably influence the results of the trial
9. Participation in another trial with an investigational drug within two months prior to administration or during the trial
10. Current smoker
11. Alcohol abuse (more than 60 g/day)
12. Drug abuse (positive urine test for illicit prescription or non-prescription drugs or drugs of abuse).
13. Blood donation (more than 100 mL within four weeks prior to study drug administration or during the trial)
14. Excessive physical activities (within one week prior to study drug administration or during the trial)
15. Any laboratory value outside the reference range that is of clinical relevance at screening, according to the judgment of the investigator
16. Inability to comply with dietary regimen required by the protocol
17. Infected with hepatitis B or hepatitis C viruses (defined as either being hepatitis B surface antigen, or hepatitis C antibody positive