Introduction. Management of primary health care (PHC) systems in less developed countries is often impeded by factors such as poorly trained personnel, limited financial resources, and poor worker morale. This study explored the ability of local-level PHC supervisors in rural Nigeria to use quality assurance (QA) management methods to improve the quality of the PHC system. Methods. PHC supervisors from Bama Local Government Area were trained for 3 days in the use of QA methods and tools. The supervisors targeted the supervisory system and the health information system (HIS) for improvement. Health worker performance in diarrhoea case management was assessed, using a simulated case, to measure the impact of supervision. A HIS audit assessed data collection forms used by 17 PHC facilities. Gaps in quality were monitored over a 2-month study period and flaws in work processes were modified. Results. PHC supervisors introduced a checklist during monthly visits to facilities to monitor how workers managed cases of diarrhoea. Performance in history-taking, physical examination, disease classification, treatment and counselling improved over the evaluation period. The HIS audit found that a variety of reporting forms were used at PHC facilities. After HIS reporting was standardized, the number of health facilities using a daily disease registry significantly improved during the study period. Conclusions. QA management methods were used by PHC supervisors in Nigeria to improve supervision and the HIS. QA management methods are appropriate for improving the quality of the PHC in Nigeria and in other less developed countries where at least a minimal PHC infrastructure exists.