Novels immuno-interactive fragments of the (alpha)C portion of a mammalian inhibin alpha subunit are disclosed, together with their variants and derivatives for producing antigen-binding molecules that are interactive with said (alpha)C portion, which are chemically well defined and which can be produced in commercially significant quantities. The antigen-binding molecules of the invention can be used for the detection of a mammalian inhibin and for the treatment and/or prevention of conditions associated with aberrant levels of a mammalian inhibin.