Private Sub ComboBox1_DropButtonClick()

'Подключения к SQL Server 
Dim rst As ADODB.Recordset
Dim con As ADODB.Connection
Dim Sheet1 As Worksheet

Set Sheet1 = ActiveSheet
Set con = New ADODB.Connection
Set rst = New ADODB.Recordset

'Строка подключения
ConnectionString = "Provider=SQLOLEDB;Data Source=KTK;" + _
"Initial Catalog=MAX101elek;user id=su;password=123"
con.Open ConnectionString

rst.ActiveConnection = con

'Запрос
sqlString = "SELECT rthed_item FROM rthed "

rst.Open sqlString
i =  0 

' Заполнение ComboBox
 Do Until rst.EOF
 ComboBox1.AddItem
 ComboBox1.List(i) = rst.Fields( 0 ).Value
 rst.MoveNext
 i = i +  1 
 Loop
 
rst.Close
con.Close

End Sub