One part of the render layer glowing? Take a look at this pic. I want only the eyes to glow without the armor glowing too (The armor got a glossy shader).
How can I do that?
Use a pass index on the material for the eyes.



Enable material index on the layer passes.


Add a ID mask on the compositor and use the number of your material pass index to create a mask for the glow.




EDIT

To make the glow yellow you can add color to the mask and change the final mix node's mode to add: