This study will assess how safe ABBV-552 is and how ABBV-552 moves through the body of adult healthy Japanese and Han Chinese participants. Adverse Events will be assessed.

ABBV-552 is an investigational drug being developed for potential treatment of Alzheimer's disease (AD). Approximately 18 adult healthy Japanese and Han Chinese volunteers will be enrolled in 2 sites in the United States.

Japanese participants assigned to Arm 1 will receive ascending doses of ABBV-552 oral capsules once every week for 3 weeks. Han Chinese participants assigned to Arm 2 will receive oral ABBV-552 capsules on Day 1. All participants will be followed for 30 days after their last dose.

Participants will be confined for 22 days or 8 days depending on the Arm they are assigned to. Adverse Events and blood tests will be performed.

Inclusion Criteria:

- Japanese participants must be first- or second-generation Japanese of full Japanese parentage. First-generation participants will have been born in Japan to two parents and four grandparents also born in Japan of full Japanese descent. Second-generation participants born outside of Japan must have two parents and four grandparents born in Japan of full Japanese descent. All participants must maintain a typical Japanese lifestyle, including consuming a typical Japanese diet.

OR

• Han Chinese participants must be first-generation Han Chinese of full Chinese parentage residing outside of China for less than 5 years. Participants must maintain a typical Chinese lifestyle, including consuming a typical Chinese diet.

Exclusion Criteria:

- Has no other clinically significant and/or unstable medical conditions or any other reason that the investigator determines would interfere with the participant's participation in this study or would make the participant an unsuitable candidate to receive ABBV-552.