An important consideration in evaluating regional networks of conservation areas is their suitability for maintaining the defensibility and viability of conservation targets over the long term.  We determined the conservation suitability of land units in the interior Columbia River basin (ICRB) using a knowledge base (KB) constructed with Ecosystem Management Decision Support software.  The KB used fuzzy logic functions to represent hypothesized relationships of ecosystem states and processes to the suitability of land units.  Suitability ratings, expressing the degree to which conditions in a land unit were suitable for conservation purposes, were produced by evaluating the KB for a set of land attributes that included land use condition, road density, land unit size, and departure of vegetation and disturbance regimes from historical conditions.  We categorized suitability ratings derived from the KB by ownership, conservation status, and elevation class in the ICRB.  Ownership categories varied widely in suitability, with the highest percentages observed for National Park Service and US Forest Service land, and the lowest percentage for private land.  Suitable land (10% of the ICRB) was evenly split between conserved and not conserved categories.  Fifty percent of suitable land was conserved, and 40% of conserved land was suitable.  Among ownership categories, conserved US Forest Service land contained the highest percentage (25%), and conserved private land the smallest percentage (<1%) of suitable land.  The percentage of conserved land in an ownership that was suitable ranged from 51% (National Park Service land) to 10% (private land).  Our results indicated that not all lands with conservation status have suitable ecological conditions, as we have defined suitability, for long-term persistence of targets of conservation.  In addition, many areas with suitable conditions exist outside conserved lands in the ICRB.