Text in merged cells does not make the row height autosize/fit, even with
WrapText.

How best to fix will depend on how much you know about 'required' heights of
other cells in the row. In the simplest scenario start by setting the row's
height to default, and some/all of this

' trap original height
rng(1).MergeArea.MergeCells = False
rng.HorizontalAlignment = xlCenterAcrossSelection
rng(1).value = sLongText
rng.WrapText = True
' might need to autofit the row here
Ht = rng(1).Height
if origHeight > Ht then Ht = origHeight
rng.HorizontalAlignment = xlLeft
rng(1).EntireRow.RowHeight = Ht ' if mergearea is only one row

Of course simply doing the above might mess up larger heights in other
merged cells, so how much you'll need to check will depend on what you've
got.

From memory a macro by Jim Rech is often recommended to autofit merged cells
(search this group)

Regards,
Peter T