Call web-service on changeFocus or onChange of textfield in MVC's view

Hello there,

I am using ASP.NET MVC 1 with .NET 3.5 SP1.
I am trying to call a web-service whenever focus moves away from a textField and then populate another textField based upon the return value of web-service. i.e through Java script or something.

Secondly, I do not want to refresh the whole screen to display the result of called web-service. Is there a simple way to achieve the above 2 things.

Thanks