Java APIs

hi folks,
if i try to run normal rmic on the class, stub class is generated perfectly but if i try by using ant it says class not found exception. this is what i am using for ant

<target name="rmic">
<mkdir dir="build/classes"/>
<rmic classname="com.services.serviceimpl" base="build/classes/" />
</target>

from same folder if i try to execute rmic com.services.serviceimpl on command prompt it works fine.. do i need to set some classpath in ant or am i missing some this else.

thanks in advance