<<Disclaimer: Verify this information before applying it to your situation.>>

Here's a quick and easy test you can do at home to see if you might have
hypochlorhydria (low stomach acid):

http://www.drdebe.com/BAKESODA.htm

The Heidelberg capsule test is described here:

http://www.healthy.net/library/books/textbook/section2/heidel.pdf

A very recent book by Dr. Jonathan V. Wright on low stomach acid looks
interesting.  I haven't yet gotten a copy to read.  It's available at
www.bn.com, www.amazon.com, www.bordersbooks.com, etc.:

http://www.mevans.com/acid.html