The PROLOGUE project constitutes a first step for understanding the methodology in- volved in carrying out naturalistic driving (ND) research. ND is defined in Deliverable 1.1 as “...unobtrusively observing normal drivers in their normal driving context while driving their own vehicles.” In order to clarify this methodology, 5 different field trials set in different parts of Europe have been performed. These trials use different ap- proaches, instrumental, and portray different goals. The common goal is a picture of the possibilities, drawbacks and potential applications of ND research. This document reports the PROLOGUE Field Trial in Valencia, Spain. This trial uses a highly instrumented car named ARGOS for evaluating the on-road behaviour of a small sample of drivers using in-vehicle information systems. The report includes a descrip- tion of the capabilities and technology of the ARGOS car, a description of a field trial planned to evaluate the use of a navigator while driving, the logistic and technical chal- lenges of this field trial, and the lessons learnt for future studies using this methodology and equipment. We regard the experience gained running this field trial as very valuable. The ARGOS car has shown to be potentially useful in the context of naturalistic observation studies. However, we have also realized that without a deep knowledge of its characteristics, results may not be as satisfactory as would be desirable.