Save PS CS5 psd file to pdf retaining transparency

I’m having difficulty saving a psd file that contains transparent layers to a pdf. The pdf file converts the transparency to a white background. Using PS CS5, I’ve tried saving the file as a PS PDF trying a number of setting permutations but can’t get the pdf to save the tranparency.

I am on a very tight deadline and need to send the files to a commercial printer later today. Your help in saving my pdf transparencies is appreciated.