H4K, your solution does not work because SSRS 2008 will not allow to have multivalue parameter and allow null value checked.

What I got is this:

CapPARAM Parameter Query:

SELECT DISTINCT ISNULL(cap.title, '') AS Captitle, ISNULL(cap.title, 'NULL') AS CaptitleDesc, cha.title AS Expr1

FROM ABC

WHERE (chap.title = @ChapPARAM)

CapPARAM Parameter Properties:

Allow Multivalue

Available Values: Value field: Captitle , Label field: CaptitleDesc.

Dataset Query

SELECT DISTINCT chap.title, cap.title AS Expr1, cap.ed_pecent

FROM ABC

WHERE (chap.title = @ChapPARAM) AND (ISNULL(cap.title, '') IN (@CapPARAM))

ORDER BY chap.title

What I need is to enable the report user to not interact imperatively in all of the parameters, but he does have to select values from the first one.

Need solutions here, Thanks

Best Regards!