referring to a particular material

I am wanting an objects texture to cycle through over time and I have this working on objects with only one material attached but need it to work on an object which has more than one material. How do i refer to the particular material? It won't allow me to use

 renderer.material[0].mainTexture

This is the entire script:

 var textures : Texture2D[];

var delay = 1.0; var textureCounter = 0;

function Start () { InvokeRepeating("CycleTextures", delay, delay); }

function CycleTextures () { textureCounter = ++textureCounter % textures.length; renderer.material(0).mainTexture = textures[textureCounter]; }

thankyou