Saab 900 headlight problem?

I am having an electrical problem with my 1992 Saab 900. The regular low-beam headlights are not working. I don't think they're blown, because this has happened before and they started working again. Parking lights, and all other lights are working fine. High-beam headlights work, but you have to hold the lever or else the high-beams go off. When the low-beams were working, the high-beams would engage fully and you would not have to hold the lever. I have checked the headlight fuses, and none are blown. Could this be a relay problem, or is it something else?

Thanks for your help!