This paper describes an investigation in progress into the searching behaviour of end-users and how it is affected by interface design. The project focused on qualitative data gathering and heavily relies on thinkaloud protocols. 65 end-users were observed searching a bibliographic database ( Medline) in their natural setting. The two most commonly used commercial versions of Medline were selected as experimental variable (OVID for Windows and WinSPIRS)- both use an underlying Boolean system and a Windowsbased interface, but present fundamental differences in terms of the use and the presentation of searching tools and results presentation. Marchionini’s model of information seeking (1995) was used as a framework. The results showed that there are some discrepancies between this model and the behaviour observed. The results of the comparison of searching behaviour with the two systems have shown some fundamental differences, but also have provided some areas of similarities in behaviour which seem to indicate that there could be some genuine end-user characteristics which are independent of system and interface design.