If you are interested in the sleep effects from ZMA then it is the magnesium that is what you are interested. If you are zinc deficient (which seems to correlate with reduced testosterone) then the zinc will be beneficial. Though this is unrelated to your question I will point out that ZMA does not raise your test levels it can only normalize them by overcoming a deficiency. As I said I know that is unrelated to your question but I thought I would toss it in because it is a common misconception associated with ZMA. Also, another interesting thing about zinc suplimentation is it was recently found to increase insulin sensitivity in non-deficient, insulin-resistant obese women. Just an interesting little extra that is worthy of consideration.