Object disappearing across pages

Still working The Shopping Cart From Hell (tm). My cart object is very simple: var $items; var $cart_id; function add($sell_price,$qty,$shipping,$tax,$productid,$short_desc,$note) { echo "current ".$this->cart_id; echo "current".$this->items; if (isset($this->items[$productid])) //if it is already in the cart, don't add a new occurrence, just update the total quantity { $this->items[$productid]["quantity"] += $qty; } else { $this->items[$productid]=array( "price"=>$sell_price, "quantity"=>$qty, "shipping"=>$shipping, "tax"=>$tax, "desc"=>$short_desc, "note"=>$note); } } //end add //a lot of other methods }//end class Cart The object is defined as a session variable in an include file, which is required_once in all scripts. The class definition is required_once also. There is a main.php which handles all the user interaction, db lookups etc, and passes the info on to the cart methods. What's happening is that the cart object seems to be destroyed every time, although it's not hitting the code that creates a new cart. The property $this->cart_id stays set all through, but if I try to echo $this->items, I get: 'Undefined property: items' in both the cart.php and the main.php (where I call $sess_cart->items). This is driving me insane because I know it should be very very simple. I've read all the online stuff I can find and this should work without having to serialize/unserialize (I'm using php 4.06). Can anyone spot something I'm doing wrong? Thanks, Sheila