This two-part study is designed to assess the safety, tolerability, and PK of gantenerumab in healthy volunteers. Part I (dose escalation) will randomly assign participants to receive a single blinded SC dose of gantenerumab or placebo. Part II (PK extension) will randomly assign participants to receive a single open-label SC dose of ganenerumab at different dose levels according to safety assessments from Part I.

Inclusion Criteria:

• Healthy males 18 to 45 years of age, inclusive
• Body mass index (BMI) 20.0 to 32.0 kilograms per meter-squared (kg/m^2), inclusive

Exclusion Criteria:

• History of cancer or any clinically significant disease affecting one of the major organ systems
• Prior administration of gantenerumab
• Clinically significant laboratory test results
• Clinically relevant history of hypersensitivity or allergic reaction following exposure to a drug, food, or environmental agent
• Known hypersensitivity to gantenerumab or excipients of study drug formulation
• Abnormal skin condition or potentially obscuring tattoo, pigmentation, or lesion in the area intended for SC injection
• Familial history of early-onset Alzheimer's disease