It is possible to generate an iso-surface from grid data read from a Gaussian cube file through the "Grid Data Surface Dialog" (Surfaces-Grid Data menu item).

This dialog box shows the information about the current dataset in the read-only Grid Data section.
The step multiplier (dafault is 1) can be increased to decrease the resolution of the generated surface for faster surface generation.
The rendering style can be changed after the surface has been generated.
To generate the surface simply press on the Generate button.
To remove the surface press the Remove button which is enabled only if a surface has been generated.
Checking the "Real-time Update" checkbox will cause a surface to be re-generated without having to press the Generate button each time any value in the dialog box changes.