How to disable a Field (FORMS 6i) in runtime?

[zeeshansohail]

I am developing a Database in ORACLE.

I have Master/Detail relationship between two tables named as BILL (Master Table) and DETAIL_DETAIL (Detail Table).

Master Table BILL contains product information like Bill_Id, ProductCode, ProductName, and BILL_DETAIL table contains Bill_Id, Sr_No, BillAmount, CompanyInfo and Product_Category.

I am developed Forms using DEVELOPER 2000 FORMs 6i,
The problem states that in some Products, Companies information should be added and in some Products, Companies Information is not needed to be added.

Keeping in view of this, I want whenever I select such Products which do not need any Companies Information. The Companies List Box should automatically be disabled.
Also whenever I select Products which should contain Companies Information, the Companies List Box should be enabled automatically.

Please help me to solve out the problem

Thank you in advance.