How to pass more than one parameter to SQL script

I have a UNIX script to call a SQL script:

   MaxWorkflowCases=$1
   PriorityLimit=$2
   sqlplus $SQLPLUS_SIGNON @$SQLPLUS_DIR/rccrwf.sql $MaxWorkflowCases $PriorityLimit

The SQL script:

   EXECUTE create_wf_cases_pr ('&1' '&2');

Please help. I got the following error:

  old 1: begin create_wf_cases_pr ('&1' '&2'); end;   new 1: begin create_wf_cases_pr ('100' '500'); end;

  begin create_wf_cases_pr ('100' '500'); end;

  *
  ERROR at line 1:
  ORA-06550: line 1, column 33:
  PLS-00103: Encountered the symbol "500" when expecting one of the following:
. ( ) , * @ % & | = - + < / > in mod not range rem => ..
  an exponent (**) <> or != or ~= >= <= <> and or etc.   The symbol "." was substituted for "500" to continue.

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Best regards,