property Items.CellData([Item as Variant], [ColIndex as Variant]) as Variant

Retrieves or sets the extra data for a specific cell.

Item as Variant A long expression that indicates the item's handle.
ColIndex as Variant A long expression that indicates the column's index, a string expression that indicates the column's caption or the column's key.
Variant A variant expression that indicates the cell's user data.

Use the CellData to associate an extra data to your cell. Use ItemData when you need to associate an extra data with an item. The CellData value is not used by the control, it is only for user use. Use the Data property to assign an extra data to a column. Use the SortUserData or SortUserDataString type to sort the column based on the CellData value. Use the CellValue property to specify the cell's caption.

Note: A cell is the intersection of an item with a column. All properties that has an Item and a ColIndex parameters are referring to a cell. The Item parameter represents the handle of an item, and the ColIndex parameter indicates an index ( a numerical value, see Column.Index property ) of a column , the column's caption ( a string value, see Column.Caption property ), or a handle to a cell ( see ItemCell property ). Here's few hints how to use properties with Item and ColIndex parameters:

G2antt1.Items.CellBold(, G2antt1.Items.ItemCell(G2antt1.Items(0), 0)) = True
G2antt1.Items.CellBold(G2antt1.Items(0), 0) = True
G2antt1.Items.CellBold(G2antt1.Items(0), "ColumnName") = True