Django: using <select multiple> and POST

I'm using something like this in my template

<select multiple="multiple"  name="services" id="services" size="5">
    {% for service in services %}
        <option value="{{service.id}}">{{service}}</option>
    {% endfor %}
</select>

When I view the POST data in Firebug or the Django debug, I see it only sends one value. Am I doing something wrong or misunderstanding a concept?