Well i guess you use the wrong helper here. Remote-function doesn't automacigally take the value of the selected option and sends it in params i think. You took the code from the Rails API docs i assume. Your controller code might be helpful too
You should try observe_field:
<select id="client_gender" name="client[gender]"> <option value="">- Select -</option> <option value="Male">Male</option> <option value="Female">Female</option> </select> <% = observe_field "cliend_gender", {:url => {:action => change}, :on => "changed"}
This should take the "value" of the <select> tag and pass it in the params hash