After ten years researching nutrition at the Max Planck Institute in Tanzania in the 1960s, he joined the World Health Organization in 1974 for a period of seven years as regional advisor for nutrition emergencies and primary health care in southern Africa. During the 1980s Kreysler worked in the AIDS Department of WHO’s Geneva headquarters, later joining WHO’s policy unit for emergency relief operations. After the Rwanda crisis in 1994 he became senior medical officer and health policy advisor for the International Red Cross (IFRC). He was awarded the Red Cross Public Health Prize in 2009 for “outstanding visionary work in the elimination of measles”. He is currently involved with People’s Health Movement as an evaluator in the context of the current WHO reform process.