AIMS: To study the context of an intervention programme, including possible competing demands between an intervention and other health service assignments, and to develop a measure of intervention intensity. METHODS: Data used include questionnaires and interviews with intervention staff, protocols, and reports from the intervention programme, and cross-sectional health surveys. A new Intervention Intensity Score (IIS) is used as an indicator of the intensity of the intervention. RESULTS: Initially the intensity of support and activity of the programme was high and some cardiovascular risk factors such as cholesterol and daily smoking declined. There were favourable allocations of resources in the setting and enthusiasm. Later, disturbing changes in the organisation, competing demands within Primary Health Care (PHC), and an incipient decline of the intervention intensity occurred. These changes accelerated and finally the intervention intensity faded out, parallel to unfavourable risk factor changes. The Intervention Intensity Score (IIS) is useful as an indicator in the interpretation of programme effectiveness. CONCLUSIONS: The amount and quality of support, the intervention process itself, and the intervention intensity were determining factors of the achievements of this intervention programme. The IIS measure used in this study provides a feasible way to interpret and understand achievements and shortcomings of the intervention programme.