How to make button readonly?

[lost]

I need to make a button readonly or not clickable...i was informed on the following but it only works for textfields not buttons. Anyone??
echo '<INPUT TYPE=button VALUE="Modify" READONLY="readonly" NAME="modifybutton" />';

[imaginemn]

Try using the following:

<INPUT TYPE=button VALUE="Modify" disabled="disabled" NAME="modifybutton" />

[lost]

Thank you!