no 18S band on RNA agarose gel - (Apr/20/2009 )

In order to check RNA purity and integrity before northern blot, I ran the samples on a 1% agarose gel.
On the gel, there was no 18S band while 28S band was present. I ran the gel again thinking I made the gel incorrectly, but the results were the same. Doesn't seem like a degradation problem since 28S band is intact. Anyone have any idea as to why this is occurring?

You did a formamide/formaldehyde denaturing gel??