By distributing the user interface between devices like a PDA and a PC, one can utilize the best characteristic from each device. This thesis has investigated what conceptual models and interface metaphors one should use when designing systems using handheld computers and PCs together. This has been done by exploring the design space of the devices, resulting in seven interface metaphors that have been adapted to a hospital case. Based on results from a focus group session and an interview, several prototypes based on the interface metaphors have been developed. These prototypes all enable a physician to display x-ray images on a patient terminal by using a PDA. In a usability test experiment the users’ actions and think-aloud protocol when using the prototypes have been captured and analyzed to find their mental models. The analysis has resulted in four general metaphors on which users internalize when using handhelds and PCs together. A design process using the user’s mental models as a basis for the creation of the conceptual model is presented. The thesis concludes with that the general metaphors found can be a good basis for the design of a conceptual model and ends with general guidelines for systems using handhelds and PCs together. Keywords: Handheld, PC, conceptual model, mental model, metaphor, design process, usability test, card sort.