Any way to trace a SQL statement from PL/SQL

I am trying to trace a statement after passing in parameters. How can I do that with SQL Plus?

Thanks,
Kim

From a SQL prompt type
set autotrace on

Unable to verify PLAN_TABLE format or existence
Error enabling EXPLAIN report
Cannot find the Session Identifier. Check PLUSTRACE role is enabled
Error enabling STATISTICS report

Run script utlxplan.sql, ususaly in directory \rdbms\admin.

From SQL propt type: set autotrace on explain