Okay, I did two with two different samples of urine with the same result. Now that I know it wasn't the dilution doing it, I'll try again. (Have to wait till I have to pee haha) Checked the expiration and it's January 2012 on all of em. None of the reviews on Amazon mention this problem, and almost all have had excellent results with them so I doubt it's the strips themselves unless its a bad batch. I guess there's probably a reason they send you 10 for 7 bucks, bound to be a few bad apples in there. I'll let you know what happens on my next couple.