FilterType in ASP.NET Ajax FilteredTextBox will have the following options:
1. Numbers
2. LowercaseLetters
3. UppercaseLetters
4. Custom
You can specify more than one options as a comma-separated combination of them.
If Custom is specified, the ValidChars field will be used in addition to other settings such as Numbers.
Refer the following link.
http://www.asp.net/ajax/ajaxcontroltoolkit/Samples/FilteredTextBox/FilteredTextBox.aspx