From today’s Register:

Iowa campaign strategists for Democrats Hillary Clinton and Barack Obama have said turnout on caucus night of 150,000 is reasonable to expect, and would be an increase of about 20 percent over 2004 participation. State GOP officials say publicly they hope participation exceeds the 2000 turnout of 86,000, while some campaign strategists are suspecting it will be lower.

According to the Iowa Secretary of State, as of last month, there are 575,025 “active registered Republicans,” and 602,947 “active registered Democrats.”