Package gstat allows 3D interpolation. It doesn't accept a 3D array directly; you'll have to provide it as x1 y1 z1 obs1 x2 y2 z2 obs2 etc, e.g. by using expand.grid. Or, you may want to try out the classes provided by package sp, which allow for more than 2 dimensions in case of points and grids. -- Edzer