correlation between two time serials

Hi, there,
   I'd like to get a statistics to reflect the correlation of two time
serials observations. for example, one time serials over time 1 to 20, and
another one from same time points from 1 to 20. I need one scalar satistics
as a correlation of these two observations.

Thank you and have a good weekend!

Jieping Zhao
PhD student in Bioinformatics, NCSU
Lab homepage: http://coltrane.gnets.ncsu.edu/index.html