Differences in levels of utilization vary and are a function of socio-economic and geographical factors. This paper presents the results of a questionnaire study involving twelve GP practices in Northamptonshire, UK, of factors which affect access and utilization in asthmatics and diabetics; these groups were selected to control for differences in utilization behaviour, as a result of different aetiologies. The questionnaire sought data on: residential location of patients, utilization characteristics of primary health-care, personal circumstances and mobility and hindrances to access and utilization. Key themes were identified relating to age, gender, social class, employment, ethnicity and proximity to the GP surgery. The young, elderly and females report higher rates of utilization, as do nonmanual workers and those who are unemployed. However, accessibility and utilization vary greatly in response to mobility and locational characteristics; these variations tend to be masked by data on overall rates of usage. Optimal scaling techniques were used to investigate the interactions between the factors affecting accessibility and utilization, and to characterize patients in terms of their levels of utilization. Results confirmed that current service provision afforded a differential level of service to patients, which does not directly reflect their level of need.