Get the max(value1, value2, value3) from a table

Greetings,

Version: PostgreSQL 8.0.13 on i686-pc-linux-gnu

I have a table test(col1, col2, col3)

For each row, I'd like to get the "max"(col1, col2, col3).

For example, test(1, 5, 2)
test(8, 1, 3)
test(12, 1, 1)

select ?max?(col1, col2, col3) as result;
will return

result
-------
5
8
12

(3 rows)

Thanks!
Ly.