Occasionally, we respond to questions. As in the following case:
Dear Dr. Info:
Why does my pee smell like that?
Signed,
Concerned
Dear Concerned:
Without more detail, it’s hard to know for sure. But my guess is that you ate asparagus recently. That’s because studies by the Urine Institute have found that more than 90 percent of questions about micturation odors are related to asparagus consumption. And indeed, these observations appear in literature from ancient times. Achilles complains about the smell of Agamemnon’s “offensive green stream” after a feast of braised asparagus (“The Iliad,” Book XIV) and retires to his tent until the air clears. Much later, Voltaire called the liquid aftermath of asparagus consumption one of the delights of life, deeming the attendant aroma le grand phunque.
Knowing you, you want more than just my guess that asparagus is involved. OK, then–let’s assume it’s asparagus. Now that we’ve done that, we can ask, “why does asparagus make your pee smell like that?”
The answer is surprising (to me, anyway): Although research has zeroed in on certain chemicals and metabolic processes that apparently play a role in producing the funk, there is no universal agreement about the source or the cause; about whether everyone produces smelly urine after an asparagus party or only some people; or whether the real issue is whether everyone has the olfactory equipment needed to smell asparagus pee.
Here are some sources:
Asparagus, in the Wikipedia (see the section on asparagus and urine).
Why does asparagus make your pee smell funny?, from The Straight Dope.
How Does Asparagus Make Urine Smell?, from eHow.com.