From this link:
There are two types of formatting:
Character (which can apply to one or
more characters) and Paragraph (which
always applies to one or more
paragraphs). You can find these
settings in the Options bar (when the
Text tool is selected in the Tool
palette) or in the Character and
Paragraph palettes.
Leading (“ledding”) determines the
amount of space between lines in a
paragraph. (...) If you want the leading to
be consistent throughout a paragraph,
you should either select every
character in the paragraph before you
set the leading in the Character
palette, or you should apply the
leading while the text layer is
selected in the Layers palette (but no
text on the layer is selected).
