datagrid1.DataSource = datatable1
For index As Integer = 0 To datatable1
Dim Cmb As New DataGridViewComboBoxCell()
Cmb = CType(datagrid1.Rows(index).Cells("fieldname"), DataGridViewComboBoxCell)
Cmb.Value = datatable1.Rows(index)("PartClaimType").ToString()
Next