Cor's right...you can use ListBox1.FindString. It will return the Item number. You can use the that item number to determine if a word is already in the ListBox or not. Just off the top of my head:
[ltr]Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim x As Integer = -1
x = ListBox1.FindString(TextBox1.Text)
If x > -1 Then
'dont add
MsgBox("Found at " & x.ToString)
Else
'code to add goes here
End If
End Sub[/ltr]
[ltr]Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim x As Integer = -1
x = ListBox1.FindString(TextBox1.Text)
If x > -1 Then
'dont add
MsgBox("Found at " & x.ToString)
Else
'code to add goes here
End If
End Sub[/ltr]