My wife and I figured this out by ourselves back in the '80s. For a while we couldn't pinpoint why our urine smelled so strong at different times. At first we thought it was from eating steak because -as it turned out - we usually had asparagus when we had steak. We finally narrowed it down to the asparagus. Our hypothesis was confirmed after my wife heard a radio report about the reaction which included the details mentioned in the post of how only some of the population (about 40%) produce the odor and only some people can smell it. This has led to some interesting (yet cautious) dinner conversations while dining with friends and when asparagus is on the menu. Precious10 is right, the reaction time between eating asparagus and one's urine presenting the odd odor is very rapid (sadly, I must admit my wife and I have had races to this effect). For me the odor is metallic and/or chemical in nature, fairly strong, but not offensive. Others have reported it to smell like rotten cabbage. I don't think I'd like that.

Hi, I am in the 4th grade and I am doing my science fair project on, "Does Asparagus make your pee smell?" I am trying to come up with a questionnaire for my test subjects to answer. Like age, gender, medical history, medicines taking. Can you help me with any other questions I might need to ask. Thanks in advance.
Hunter