BACKGROUND: In an attempt to achieve universal health coverage, Nigeria introduced a number of health insurance schemes. One of them, the Formal Sector Social Health Insurance Programme (FSSHIP), was launched in 2005 to provide health cover to federal government and formal private sector employees. It operates with two levels of purchasers, the National Health Insurance Scheme (NHIS) and health maintenance organisations (HMOs). This study critically assesses purchasing arrangements between NHIS, HMOs and healthcare providers and determines how the arrangements function from a strategic purchasing perspective within the FSSHIP. METHODS: A qualitative study undertaken in Enugu state, Nigeria, data were gathered through reviews of documents, 17 in-depth interviews (IDIs) with NHIS, HMOs and healthcare providers and two focus group discussions (FGDs) with FSSHIP enrolees. A strategic purchasing lens was used to guide data analysis. RESULTS: The purchasing function was not being used strategically to influence provider behaviour and improve efficiency and quality in healthcare service delivery. For the purchaser-provider relationship, these actions are: accreditation of healthcare providers; monitoring of HMOs and healthcare providers and use of appropriate provider payment mechanisms for healthcare services at every level. The government lacks resources and political will to perform their stewardship role while provider dissatisfaction with payments and reimbursements adversely affected service provision to enrolled members. Underlying this inability to purchase, health services strategically is the two-tiered purchasing mechanism wherein NHIS is not adequately exercising its stewardship role to monitor and guide HMOs to fulfil their roles and responsibilities as purchasing administrators. CONCLUSIONS: Purchasing under the FSSHIP is more passive than strategic. Governance framework requires strengthening and clarity for optimal implementation so as to ensure that both levels of purchasers undertake strategic purchasing actions. Additional strengthening of NHIS is needed for it to have capacity to play its stewardship role in the FSSHIP.