Private sCat As New Scripting.Dictionary
...
[irgendwo in einer sub]
  With Rs1
    .MoveFirst
    Do While Not .EOF
      MsgBox "Hier 1: " & .Fields("key"), vbInformation
      If sCat.Exists(.Fields("key")) Then
        MsgBox "Hier 3: " & .Fields("key"), vbInformation
        sCat(.Fields("key")) = sCat(.Fields("key")) & " " & .Fields("val")
      Else
        MsgBox "Hier 2: " & .Fields("key"), vbInformation
        sCat.Add .Fields("key"), .Fields("val")
      End If
      .MoveNext
    Loop
  End With