Despite increasing interest in computerised decision support in general practice, there is little evidence about how such systems would be used. This study examined the use made by 128 GPs of a new computerised medical reference resource designed to be used as decision support tool. It found that, on average, GPs used the resource 1.35 times a day (range 0_12). The most common information used related to clinical problem solving. Some parts of the system, such as those relating to epidemiological information, appeared to be used infrequently. The reasons for the wide variation in the reported use of the system require further investigation.