It seems to work like this:

InitialenRemote initiaal = null;
Context context = new InitialContext();
UserTransaction userTran = (UserTransaction)context.lookup("UserTransaction");
try{
 userTran.begin();

 String strInitiaal = initialenForm.getInitiaal();
 Object einRef = context.lookup("Initiaal");
 InitialenHomeRemote home = (InitialenHomeRemote)PortableRemoteObject.narrow(einRef, InitialenHomeRemote.class);
 initiaal = home.create(strInitiaal);

 userTran.commit();
}catch(Exception e){
 userTran.rollback();
 e.printStackTrace();
}