Specific object collision

Hi all, I have set up a collision script so that one a specific game object "missile" collides with another game object "roid" a particle is instantiated at the "roids" position. For some reason no matter what object collides with the roid the particle is instantiated. How can I get the particle to fire ONLY if the objects colliding are the "missile" and the "roid"? Here is the code I am using for this:

var roid: Rigidbody;
var missile: Rigidbody;
var missileExplodeFire: ParticleEmitter;
var missileExplodeFireRed: ParticleEmitter;
var missileExplodeRock: ParticleEmitter;

function OnCollisionEnter (collision : Collision) {

    if (collision.gameObject.missile == collision.gameObject.roid)
    {
        missileExplodeFire = Instantiate(missileExplodeFire, roid.position, transform.rotation);
        missileExplodeFireRed = Instantiate(missileExplodeFireRed, roid.position, transform.rotation);
        missileExplodeRock = Instantiate(missileExplodeRock, roid.position, transform.rotation);
        missileExplodeFire.emit = true;
        missileExplodeFireRed.emit = true;
        missileExplodeRock.emit = true;
    }
    if (!collision.gameObject.missile == !collision.gameObject.roid)
    {

    }
}

Any ideas would be greatly appreciated.

Hi all, Solved this problem by creating with tags rather than simply trying to reference the rigidbody variables missile and roid in the OnCollisionEnter function.