The IMPROVE Project is a 4-year randomized controlled trial to test the hypothesis that HMOs can improve preventive services in their contracted primary clinics by assisting clinics to implement continuous quality improvement (CQI) and an organized system for preventive services. This paper describes findings from case studies of CQI teams in two demonstration sites where the CQI approach was tested. The case study analysis is based on interviews and observations conducted about 10 to 12 months after the CQI teams began. Initial responses of clinic staff to the IMPROVE Project included a mixture of interest in CQI, enthusiasm for prevention-oriented care, concern about the burden the project might impose, and skepticism. There were two formidable barriers to change: time and inertia. Environmental changes in the parent organizations also complicated and impeded the CQI process within the clinics. The thematic analysis identified four factors that appear to be important in implementing a CQI process in a clinic setting: awareness, momentum, ownership, and communication.