parseInt will give you back digits as long as it can. In your case, you would get 11 for the parseInt value which is a number so isNaN is false. http://msdn.microsoft.com/library/default.asp?url=/library/en-us/script56/html/js56jsmthparseint.asp The example from this reference is as follows: parseInt("12abc") // Returns 12. > >I have tried the > >alert ( isNaN(parseInt(window.document.myform.RMList.value)) ); > >to figure this out. > >but it will allow me to enter this "11dd44" >this is not a number > >so what gives?