We describe a highly participatory approach to improve the design and distribution of a novel oral rehydration salts and zinc (ORSZ) co-pack to treat diarrhea in children aged younger than 5 years in Zambia.n Developing existing structures and experience across multiple sectors was key to the evolving intervention design, shared vision, resulting partnership, and sustainability.n Aiming from the outset to embed a successful product for private sector manufacture, we suppressed funder and project branding, testing the product and its value chain. nThe process led to the successful horizontal scaleup (replication/expansion) and vertical scale-up (institutionalization) of the ORSZ co-pack.