I need to populate a dropdown listbox named "sub category" once the user the clicks his desired selection in the dropdown listbox named "category" e.g. clothing has subcategories like gent's clothes and ladies clothes.

I need to know which event i have to use? Im not sure in what event i have to put my code in exactly.Could someone give me some demonstration thru code please..thanx

Use the SelectedIndexChanged event of the "Category" dropdownlist.
Jim

okay i did try onSelectedIndexChanged ="populate", embeded this value in the server control tag as : <asp:dropdownlist id="cboCat" width="150" onSelectedIndexChanged="populate" runat="server"/>.

The populate procedure is as follows:
Sub populate(sender as object, e as eventargs)
      'code to populate subcategory dropdown list box
 End Sub

But it is not working , whenever i select any other item in the category listbox the first item gets selected automatically.

I did set the AutoPostBack property to true, but with this i get the first item of the dropdown listbox selected everytime i try to select any other item i.e. if there are four items in the order clothing, food, stores, homeliving and i select stores then clothing gets selected automatically.
And even if i set AutoPostBack ="False" the same thing happens but this time only on the first click r selection it happens.

why is that? I jus want this dropdown listbox to leave with the value i selected .

Please look in to it and let me know what to do...thanx

okay let me just explain the heart of the problem. There is this dropdownlist populated with vales from SQL Server 7.0 database i.e. "clothing","food","stores" and "homeliving".
Now just the first time when the user selects any value from this list the first value "clothing" gets selected and on the status bar it comes "opening page http://maxood/5040/watal.aspx" .This means the page gets loaded again.

Now how can i stop it!!??

Here is my code for the page load event:

Dim strConnection as String = "server=Maxood;database=watal;user id=sa;password=;"
  Dim strSql as String = "Select categoryname from category"

  Dim objConn1 as New SqlConnection(strConnection)
  Dim cmdCat as New SqlCommand(strSql,objConn1)


  objConn1.Open()
  cboCat.DataSource = cmdCat.ExecuteReader(System.Data.CommandBehavior.C loseConnection)
  cboCat.DataTextField = "categoryname"
  cboCat.DataBind()



  strSql = "Select * from city"
  Dim objConn2 as New SqlConnection(strConnection)
  Dim cmdCity as New SqlCommand(strSql,objConn2)

  objConn2.Open()

  cbocity.DataSource =cmdCity.ExecuteReader(System.Data.CommandBehavior .CloseConnection)
  cboCity.DataTextField="city"
  cboCity.DataBind()

Please explain!!

When AutoPostBack is set to true on a control, the page gets posted back. You need this to be set to true in order to grab the value of the selected item in one dropdown in order to populate the second one.

For values you do not want re-populated on postback, you need an IF Not IsPostBack statement:
IF Not IsPostBack Then
 Dim strSql as String = "Select categoryname from category"

  Dim objConn1 as New SqlConnection(strConnection)
  Dim cmdCat as New SqlCommand(strSql,objConn1)


  objConn1.Open()
  cboCat.DataSource = cmdCat.ExecuteReader(System.Data.CommandBehavior.C loseConnection)
  cboCat.DataTextField = "categoryname"
  cboCat.DataBind()



  strSql = "Select * from city"
  Dim objConn2 as New SqlConnection(strConnection)
  Dim cmdCity as New SqlCommand(strSql,objConn2)

  objConn2.Open()

  cbocity.DataSource =cmdCity.ExecuteReader(System.Data.CommandBehavior .CloseConnection)
  cboCity.DataTextField="city"
  cboCity.DataBind()
End IF

End Sub

thnax a lot for this tip. I need to know what event is generated when a user selects a new item in a dropdown list box.
I have to populate the subcategories dropdown list once the user selects the item in the category listbox.For example if the categories are clothing, foods, stores and home living and the user selects clothing then the subcategory listbox should be populated with values like gents clothes, ladies clothes, etc.

Please give me an exaple through code...thanx.

I already told you. Use the selectedindex event of the category drop down list. I am not going to write code for you. Just create the event for the drop down, and place your code to populate the other drop down there.