TMC647055 is being investigated for the treatment of chronic hepatitis C infection. This is a first-in-human, double-blind (sponsor, investigator and participant do not know which treatment is given), randomized (like flipping a coin), placebo-controlled, single centre, Phase I study in healthy volunteers to examine the safety, tolerability, and plasma pharmacokinetics of increasing single oral doses and of increasing repeated oral doses of TMC647055, followed by a double-blind repeated-dose part in chronic hepatitis C virus (HCV) infected patients. The study population will consist of 45 healthy adult volunteers between 18 and 55 years of age and 10 or 20 chronic HCV-genotype 1 infected patients between 18 and 65 years of age. The single dose escalation part of the trial will include 2 panels (Panels 1 and 2) of 9 participants each. There will be 6 sessions (Sessions I to VI): panel 1 will do sessions I, III & V; panel 2 will do sessions II, IV and VI. In each session, 6 participants will receive TMC647055 and 3 participants will receive placebo with standard meals. Over 3 sessions, each participant will receive TMC647055 twice and placebo once. The dose of TMC647055 will be consecutively increased. Planned doses will be 100 mg, 250 mg, 600 mg, 1250 mg, 2000 mg, and 3000 mg of TMC647055 or placebo, administered as a single oral administration. A wash out period of at least 10 days will be respected between 2 sessions of 1 panel. Doses may be adapted pending the safety and pharmacokinetic outcome of the previous sessions but will not exceed the limit of 3000 mg. Dose increase will only occur if the previous dose is shown to be generally safe and tolerable. For precautionary safety reasons, the dose administration in sessions IV, V and VI will be staggered: the first 4 to 5 participants of the panel will receive the dose at least 24 hours prior to the second group of 4 to 5 participants. To investigate the effect of food, one single dose will be tested in fasted conditions (Session VII). The dose of TMC647055 tested in this session will be derived from the results obtained in Sessions I to V. Participants who received TMC647055 at the selected dose with standard meals in Sessions I to V will again receive TMC647055 in fasted conditions in Session VII. Participants who received placebo will receive placebo again. The multiple-dose escalation part of the trial (sessions VIII, IX and X) will include 3 panels (Panels 3, 4, and 5) of 9 participants each: panel 3 will do session VIII, panel 4 session IX and panel 5 session X. In all panels, TMC647055 or placebo will be administered during 6 consecutive days, with on Day 6 a morning dose only. Medication is anticipated to be given either every 8 hours, every 12 hours or every 24 hours. This can be changed per dosing session following the outcome of the previous session. In each multiple dosing session, 6 participants will receive TMC647055 and 3 participants will receive placebo. The multiple dose escalation part will be started when the doses of Sessions I, II, III, and IV are found to be generally safe and tolerable based upon review of the blinded safety and pharmacokinetic data. Dose increase will only occur if the previous dose is shown to be generally safe and tolerable. The initial daily dose tested in Panel 3 will not be higher than the doses tested in Sessions I to IV. After the healthy volunteer sessions, there will be 3 sessions in chronic HCV infected patients (sessions XI, XII and XIII). Session XI will be started when the doses in healthy volunteers are found to be generally safe and tolerable and a selected dose will be given every 12 hours. The total daily dose will not exceed the highest daily dose and exposure shown to be generally safe in the multiple dose escalation in healthy volunteers. The dose for session XII will be selected based on the results from session XI and will be given every 12 hours or every 8 hours. In each session, 8 patients will receive TMC647055 and 2 patients will receive placebo. TMC647055 will be given during 6 consecutive days with on day 6 a morning dose only. Session XIII will be open-label and will consist of 2 treatment arms. In treatment arm 1, 8 patients will receive TMC647055 (1000 mg twice a day) co-administered with TMC435 (150 mg once daily) for 10 days.In treatment arm 2, 8 subjects will receive TMC435 (150 mg once daily) for 6 days. Safety and tolerability will be evaluated continuously by checking illnesses and side effects, by taking blood and urine samples, by electrocardiograms and telemetry (electrical recording of the heart, only for healthy volunteers), by taking blood pressure and heart rate and by performing physical examinations. TMC647055 or placebo will be given as an oral solution, ranging from 100 to 3000 mg in the single dose part, in the multiple dose part during 6 consecutive days either every 8 hours, 12 hours or 24 hour. In sessions XI and XII, TMC647055 or placebo will be given every 8 or 12 hours at dose and frequency determined by results of the previous sessions. In session XIII, the dose of TMC647055 will be 1000 mg twice a day and TMC435 will be given as oral capsules at 150 mg once daily.