Custom item fields

How do you force a user to make a selection in a custom item field?

I have set up a custom item field as such:

Table: item
Type: single dropdown
Required: Yes
Default: "Please select"
Values:
Please select (disabled)
Option 1 (enabled)
Option 2 (enabled)

1. My product listing has an "add to cart" button shown and allows the user to add the product to the cart and proceed to registration without making a selection for the custom item field.

2. My product page allows the user to add to the cart and proceed to registration without making a selection for the custom item field.

Thanks.

(using business 1.5.6)

Thanks! That worked a treat!