Set the select control value
<html> <head> <title>Pizza</title> <script type = "text/javascript"> function flip(pizzatype) { if (pizzatype.value == "A") { document.forms["pizzaform"].topping.value = "aa"; } else if (pizzatype.value == "B") { document.forms["pizzaform"].topping.value = "bb"; } else if (pizzatype.value == "C") { document.forms["pizzaform"].topping.value = "cc"; } } </script> </head> <body> <form id="pizzaform" action="#" onsubmit="return false;"> <p> <input type="button" name="valueA" onclick="flip(valueA)" value="A"/> <input type="button" name="valueB" onclick="flip(valueB)" value="B" /> <input type="button" name="valueC" onclick="flip(valueC)" value="C" /> </p> <p>Main Topping: <select name="topping"> <option value="aa" selected="selected">Cheese</option> <option value="bb">Veggies</option> <option value="cc">Meat</option> <option value="dd">Ham & Pineapples</option> </select></p> </form> </body> </html>