The purpose of this study is to evaluate whether IMMUNATE S/D is effective and safe in the treatment of hemophilia A patients. The study consists of 3 parts: Part 1 is a pharmacokinetic comparison of IMMUNATE S/D and its predecessor IMMUNATE. Part 2 is an evaluation of efficacy and safety of IMMUNATE S/D. Part 3 is a pharmacokinetic study of IMMUNATE S/D.

Inclusion Criteria:

- Plasma factor VIII level as follows: for Parts 1 & 3: Subjects with severe hemophilia A (plasma baseline factor VIII level <= 1% measured at time of screening) for Part 2: Subjects with severe (plasma baseline factor VIII level <= 1% measured at time of screening) or moderately severe hemophilia A (plasma baseline factor VIII level <= 2% measured at time of screening)

• Males >= 12 but <= 65 years of age
• >= 35 kg body weight
• Previously treated with factor VIII concentrate(s) for a minimum of 150 exposure days (as documented in the subject's medical history)
• Evidence of a protective titer to HAV and HBV at the time of screening
• Immunocompetent as defined by a CD4+ lymphocyte count >400/mm3 and an absolute neutrophil count (ANC) >1500
• Signed informed consent obtained from subject or legally authorized representative

Exclusion Criteria:

• Documented history of inhibitor to factor VIII with a titer >= 0.8 BU
• Current evidence of inhibitor to factor VIII with a titer >= 0.8 BU, measured at the time of screening
• Abnormal renal function (serum creatinine > 1.5 mg/dL)
• HIV-seropositive individuals with any of the following at the time of screening:
• CD4+ lymphocyte count >400/mm3
• AIDS-related complex
• symptomatic AIDS Note: HIV-seropositive subjects with an absolute CD4+ lymphocyte count > 400/mm3 are eligible to participate. HIV-seropositive subjects receiving highly active anti-retroviral therapy (HAART) regimens are eligible for enrollment if they are not excluded by the above criteria
• Active hepatic disease (ALT and AST levels > 5 times the upper limit of normal)
• Clinical or laboratory evidence of hepatic cirrhosis including (but not limited to) a recent and persistent INR (international normalized ratio) > 1.4, the presence of splenomegaly and/or significant spider angiomata on physical exam, and/or a history of esophageal hemorrhage or documented esophageal varices
• Known hypersensitivity to IMMUNATE
• The subject is currently participating in another investigational drug study, or has participated in any clinical study involving an investigational drug within 30 days of study entry
• The subject is currently receiving, or is scheduled to receive during the course of the study, an immunomodulating drug other than anti-retroviral chemotherapy (e.g., a-interferon, steroids at a dose greater than 10 mg/day)
• The subject is identified by the investigator as being unable or unwilling to perform study procedures