removing items from drop down in Javascript

[lavi mendonca]

i have 2 dropdown/ list parent and child. If one of the options in the parent list is selected, then in the child listbox, i only want to display some of the options and not all the values previously displayed. If i choose some other option in the parent dropdown, then some other values should be displayed in the child drop down. But no empty row should be displayed..Could someone help out..
Thanks.