>>If you recall PRIVATE scope is hierarchical - visible down from where a variable is declared all the way into child functions/methods called. LOCAL scope is local to the function the variable is declared at. So LPARAMETERS limits the scope of the parameters - where they are visible - to the function they are declared in.
>>
>>It has nothing to do with passing by value or by reference.

Just to add to Rick's comments, what LPARAMETERS does is hide the variable from anything called by this routine. That is, the difference is relevant in this case:

MyProc1(42)

PROCEDURE MyProc1
PARAMETERS nNum

MyProc2()
?m.nNum  &&  37

RETURN

PROCEDURE MyProc2

* Refer to nNum
nNum = 37

RETURN

and:

PROCEDURE MyProc1
LPARAMETERS nNum

MyProc2()
?m.nNum && 42

RETURN

PROCEDURE MyProc2

* Refer to nNum without declaring it
nNum = 37

RETURN

In the first example, nNum in MyProc1 is changed by MyProc2. In the second, it's not.

Tamar