Photoshop :: Centering Text Vertically In Text Box

When you open a text box how do you center the text in the middle from top to bottom(vertically), not left to right. The text starts immediately in the top left corner. I need it in the center of a predefined text box size, so that if you drew a line across the center of the box from left to right, the top half of the letters  would be above the line and the bottom half would be below the center line. In other words there should be the same distance above the words to the top edge of the text box, as to the bottom of the text box, from the center.