As INSPIRE progresses to be implemented in the EU, many new discovery portals are built to facilitate finding spatial data. Currently the structure of the discovery portals is determined by the way spatial data experts like to work. However, we argue that the main target group for discovery portals are not spatial data experts but professionals with limited spatial knowledge, and a focus outside the spatial domain. An exploratory usability experiment was carried out in which three discovery portals were assessed by five participants representing the main target group “the professional outside the spatial domain”. The aim was to accept or reject our proposition that discovery portals are difficult to use for non-GIS specialists, and to identify the main obstacles in the interface. The Think Aloud Protocol was used to conduct the test. The participants were asked to perform the same search task in three discovery portals. Performance, accuracy and emotional response of the participants were assessed. Given the language constraints and the concise task the differences between the discovery portals were found to be relatively small. We conclude that for all portals indexing and underlying techniques are well implemented. The content of metadata is a point of concern. We recommend that more attention should be given to the requirements and expectations of the end-user and the discoverability of the data sets when creating metadata. But most of all the design and implementation of the client interface should be improved.