In order to obtain a better understanding of barriers to the implementation of clinical decision-support systems (CDSSs) in primary health care, we explored general practitioners' (GPs) handling of a CDSS during the implementation process. An Internet-based application for the management of chronic heart failure was used that was an adaptation of established clinical guidelines for computer use. The whole implementation process was followed closely, using a combination of different methods for data collection: repeated interviews with the five participating GPs, observations of patient visits, patient interviews, and detection of usage. We analysed the data using qualitative content analysis. The results showed that GPs' attitudes and characteristics constituted different profiles that seemed to be associated with the degree of acceptance of the CDSS. Those profiles were related to conceptions about the GPs' professional role and their attitudes towards the computer's function in disease management and in decision-making. Some additional barriers were insufficient level of computer skills and time constraints in everyday work. These findings can help us identify groups of GPs with definable needs during the implementation of a CDSS and make it easier to meet those needs with individually tailored interventions.