How to check spelling in Excel programmatically

This FAQ will help you to check word spelling in Excel using .NET. The CheckSpelling method works slightly different depending if the object is the Application, Wroksheet or Range object.

You can check spelling at application, worksheet or range level by using CheckSpelling method:

Application: It checks words using Excel spelling resources
private void DoSpellingCheck(Excel.Application app, string wordToCheck)
{
    app.CheckSpelling(wordToCheck, Type.Missing, Type.Missing);
}

Worksheet: It checks headers, footers, and objects existing on a worksheet.
private void DoSpellingCheck(Excel.Worksheet sheet)
{
    sheet.CheckSpelling(Type.Missing, true, true,
        Office.MsoLanguageID.msoLanguageIDEnglishUS);
}

Range or Cell:It checks spelling of a range or cell object.
private void DoSpellingCheck(Excel.Range range)
{
    range.CheckSpelling(Type.Missing, true, true,
        Office.MsoLanguageID.msoLanguageIDEnglishUS);
}

This method is also available in other Excel objects like named ranges, chart and controls like textbox, group box.

The sample code is in C# but can translated to VB.NET very easily, for example the application code in VB.NET will look like:
Private Sub CheckSpelling(Dim app As Excel.Application, Dim wordToCheck As String)
    app.CheckSpelling(wordToCheck)
End Sub

For more information check:
http://msdn.microsoft.com/en-us/library/aa223822(office.11).aspx