Validate textbox to be alpha only

Guys,

How can I force a textbox on an asp.net page to contain alpha and num chars only ? ie - No symbols.

When the users hit a button I am adding a record to my SQL dbase and I need to ensure they are not using symbols in certain fields.

Thanks
Bob

Use a RegularExpressionValidator control.

Thanks Glen, but what would the validation expression be ?

Thanks
Bob

This may not be spot on but it shouldn't be far away.

[^a-zA-Z0-9]